diff --git a/bare-arm/main.c b/bare-arm/main.c
index 7405ece5e8..7efcf9ab33 100644
--- a/bare-arm/main.c
+++ b/bare-arm/main.c
@@ -45,7 +45,7 @@ mp_import_stat_t mp_import_stat(const char *path) {
     return MP_IMPORT_STAT_NO_EXIST;
 }
 
-mp_obj_t mp_builtin_open(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);
diff --git a/extmod/modubinascii.c b/extmod/modubinascii.c
index 12cd266870..82f910b0e7 100644
--- a/extmod/modubinascii.c
+++ b/extmod/modubinascii.c
@@ -34,7 +34,7 @@
 #include "modubinascii.h"
 
 
-mp_obj_t mod_binascii_hexlify(mp_uint_t n_args, const mp_obj_t *args) {
+mp_obj_t mod_binascii_hexlify(size_t n_args, const mp_obj_t *args) {
     // Second argument is for an extension to allow a separator to be used
     // between values.
     const char *sep = NULL;
diff --git a/extmod/modubinascii.h b/extmod/modubinascii.h
index 94e69b18eb..0f9b82c1cb 100644
--- a/extmod/modubinascii.h
+++ b/extmod/modubinascii.h
@@ -27,7 +27,7 @@
 #ifndef MICROPY_EXTMOD_MODUBINASCII
 #define MICROPY_EXTMOD_MODUBINASCII
 
-extern mp_obj_t mod_binascii_hexlify(mp_uint_t n_args, const mp_obj_t *args);
+extern mp_obj_t mod_binascii_hexlify(size_t n_args, const mp_obj_t *args);
 extern mp_obj_t mod_binascii_unhexlify(mp_obj_t data);
 extern mp_obj_t mod_binascii_a2b_base64(mp_obj_t data);
 extern mp_obj_t mod_binascii_b2a_base64(mp_obj_t data);
diff --git a/extmod/modure.c b/extmod/modure.c
index 5843569a50..91c97bf8b7 100644
--- a/extmod/modure.c
+++ b/extmod/modure.c
@@ -115,17 +115,17 @@ STATIC mp_obj_t re_exec(bool is_anchored, uint n_args, const mp_obj_t *args) {
     return MP_OBJ_FROM_PTR(match);
 }
 
-STATIC mp_obj_t re_match(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t re_match(size_t n_args, const mp_obj_t *args) {
     return re_exec(true, n_args, args);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(re_match_obj, 2, 4, re_match);
 
-STATIC mp_obj_t re_search(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t re_search(size_t n_args, const mp_obj_t *args) {
     return re_exec(false, n_args, args);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(re_search_obj, 2, 4, re_search);
 
-STATIC mp_obj_t re_split(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t re_split(size_t n_args, const mp_obj_t *args) {
     mp_obj_re_t *self = MP_OBJ_TO_PTR(args[0]);
     Subject subj;
     mp_uint_t len;
@@ -182,7 +182,7 @@ STATIC const mp_obj_type_t re_type = {
     .locals_dict = (void*)&re_locals_dict,
 };
 
-STATIC mp_obj_t mod_re_compile(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_re_compile(size_t n_args, const mp_obj_t *args) {
     const char *re_str = mp_obj_str_get_str(args[0]);
     int size = re1_5_sizecode(re_str);
     if (size == -1) {
@@ -215,12 +215,12 @@ STATIC mp_obj_t mod_re_exec(bool is_anchored, uint n_args, const mp_obj_t *args)
     return match;
 }
 
-STATIC mp_obj_t mod_re_match(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_re_match(size_t n_args, const mp_obj_t *args) {
     return mod_re_exec(true, n_args, args);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_re_match_obj, 2, 4, mod_re_match);
 
-STATIC mp_obj_t mod_re_search(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_re_search(size_t n_args, const mp_obj_t *args) {
     return mod_re_exec(false, n_args, args);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_re_search_obj, 2, 4, mod_re_search);
diff --git a/extmod/moduzlib.c b/extmod/moduzlib.c
index 2a07f008f4..3d945abba5 100644
--- a/extmod/moduzlib.c
+++ b/extmod/moduzlib.c
@@ -49,7 +49,7 @@ STATIC int mod_uzlib_grow_buf(TINF_DATA *d, unsigned alloc_req) {
     return 0;
 }
 
-STATIC mp_obj_t mod_uzlib_decompress(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_uzlib_decompress(size_t n_args, const mp_obj_t *args) {
     (void)n_args;
     mp_obj_t data = args[0];
     mp_buffer_info_t bufinfo;
diff --git a/py/builtin.h b/py/builtin.h
index 5653c48d30..261e5a2311 100644
--- a/py/builtin.h
+++ b/py/builtin.h
@@ -28,9 +28,9 @@
 
 #include "py/obj.h"
 
-mp_obj_t mp_builtin___import__(mp_uint_t n_args, const mp_obj_t *args);
-mp_obj_t mp_builtin_open(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
-mp_obj_t mp_micropython_mem_info(mp_uint_t n_args, const mp_obj_t *args);
+mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args);
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
+mp_obj_t mp_micropython_mem_info(size_t n_args, const mp_obj_t *args);
 
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin___build_class___obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_builtin___import___obj);
diff --git a/py/builtinevex.c b/py/builtinevex.c
index cac74e94fd..74c43b1768 100644
--- a/py/builtinevex.c
+++ b/py/builtinevex.c
@@ -74,7 +74,7 @@ STATIC mp_obj_t code_execute(mp_obj_code_t *self, mp_obj_dict_t *globals, mp_obj
     }
 }
 
-STATIC mp_obj_t mp_builtin_compile(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_compile(size_t n_args, const mp_obj_t *args) {
     (void)n_args;
 
     // get the source
@@ -109,7 +109,7 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_compile_obj, 3, 6, mp_builtin_com
 
 #if MICROPY_PY_BUILTINS_EVAL_EXEC
 
-STATIC mp_obj_t eval_exec_helper(mp_uint_t n_args, const mp_obj_t *args, mp_parse_input_kind_t parse_input_kind) {
+STATIC mp_obj_t eval_exec_helper(size_t n_args, const mp_obj_t *args, mp_parse_input_kind_t parse_input_kind) {
     // work out the context
     mp_obj_dict_t *globals = mp_globals_get();
     mp_obj_dict_t *locals = mp_locals_get();
@@ -147,12 +147,12 @@ STATIC mp_obj_t eval_exec_helper(mp_uint_t n_args, const mp_obj_t *args, mp_pars
     return mp_parse_compile_execute(lex, parse_input_kind, globals, locals);
 }
 
-STATIC mp_obj_t mp_builtin_eval(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_eval(size_t n_args, const mp_obj_t *args) {
     return eval_exec_helper(n_args, args, MP_PARSE_EVAL_INPUT);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_eval_obj, 1, 3, mp_builtin_eval);
 
-STATIC mp_obj_t mp_builtin_exec(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_exec(size_t n_args, const mp_obj_t *args) {
     return eval_exec_helper(n_args, args, MP_PARSE_FILE_INPUT);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_exec_obj, 1, 3, mp_builtin_exec);
@@ -160,7 +160,7 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_exec_obj, 1, 3, mp_builtin_exec);
 #endif // MICROPY_PY_BUILTINS_EVAL_EXEC
 
 #if MICROPY_PY_BUILTINS_EXECFILE
-STATIC mp_obj_t mp_builtin_execfile(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_execfile(size_t n_args, const mp_obj_t *args) {
     // MP_PARSE_SINGLE_INPUT is used to indicate a file input
     return eval_exec_helper(n_args, args, MP_PARSE_SINGLE_INPUT);
 }
diff --git a/py/builtinimport.c b/py/builtinimport.c
index 2560ec1563..ec79357cb7 100644
--- a/py/builtinimport.c
+++ b/py/builtinimport.c
@@ -215,7 +215,7 @@ STATIC void chop_component(const char *start, const char **end) {
     *end = p;
 }
 
-mp_obj_t mp_builtin___import__(mp_uint_t n_args, const mp_obj_t *args) {
+mp_obj_t mp_builtin___import__(size_t n_args, const mp_obj_t *args) {
 #if DEBUG_PRINT
     DEBUG_printf("__import__:\n");
     for (mp_uint_t i = 0; i < n_args; i++) {
diff --git a/py/modbuiltins.c b/py/modbuiltins.c
index d1f99bb98d..53774110a8 100644
--- a/py/modbuiltins.c
+++ b/py/modbuiltins.c
@@ -48,7 +48,7 @@ extern struct _mp_dummy_t mp_sys_stdout_obj; // type is irrelevant, just need po
 // args[0] is function from class body
 // args[1] is class name
 // args[2:] are base objects
-STATIC mp_obj_t mp_builtin___build_class__(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin___build_class__(size_t n_args, const mp_obj_t *args) {
     assert(2 <= n_args);
 
     // set the new classes __locals__ object
@@ -193,7 +193,7 @@ STATIC mp_obj_t mp_builtin_chr(mp_obj_t o_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_chr_obj, mp_builtin_chr);
 
-STATIC mp_obj_t mp_builtin_dir(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_dir(size_t n_args, const mp_obj_t *args) {
     // TODO make this function more general and less of a hack
 
     mp_obj_dict_t *dict = NULL;
@@ -264,7 +264,7 @@ MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_iter_obj, mp_builtin_iter);
 
 #if MICROPY_PY_BUILTINS_MIN_MAX
 
-STATIC mp_obj_t mp_builtin_min_max(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs, mp_uint_t op) {
+STATIC mp_obj_t mp_builtin_min_max(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs, mp_uint_t op) {
     mp_map_elem_t *key_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_key), MP_MAP_LOOKUP);
     mp_map_elem_t *default_elem;
     mp_obj_t key_fn = key_elem == NULL ? MP_OBJ_NULL : key_elem->value;
@@ -305,12 +305,12 @@ STATIC mp_obj_t mp_builtin_min_max(mp_uint_t n_args, const mp_obj_t *args, mp_ma
     }
 }
 
-STATIC mp_obj_t mp_builtin_max(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+STATIC mp_obj_t mp_builtin_max(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     return mp_builtin_min_max(n_args, args, kwargs, MP_BINARY_OP_MORE);
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_max_obj, 1, mp_builtin_max);
 
-STATIC mp_obj_t mp_builtin_min(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+STATIC mp_obj_t mp_builtin_min(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     return mp_builtin_min_max(n_args, args, kwargs, MP_BINARY_OP_LESS);
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_min_obj, 1, mp_builtin_min);
@@ -375,7 +375,7 @@ STATIC mp_obj_t mp_builtin_ord(mp_obj_t o_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_ord_obj, mp_builtin_ord);
 
-STATIC mp_obj_t mp_builtin_pow(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_pow(size_t n_args, const mp_obj_t *args) {
     assert(2 <= n_args && n_args <= 3);
     switch (n_args) {
         case 2: return mp_binary_op(MP_BINARY_OP_POWER, args[0], args[1]);
@@ -384,7 +384,7 @@ STATIC mp_obj_t mp_builtin_pow(mp_uint_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_pow_obj, 2, 3, mp_builtin_pow);
 
-STATIC mp_obj_t mp_builtin_print(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+STATIC mp_obj_t mp_builtin_print(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     mp_map_elem_t *sep_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_sep), MP_MAP_LOOKUP);
     mp_map_elem_t *end_elem = mp_map_lookup(kwargs, MP_OBJ_NEW_QSTR(MP_QSTR_end), MP_MAP_LOOKUP);
     const char *sep_data = " ";
@@ -456,7 +456,7 @@ STATIC mp_obj_t mp_builtin_repr(mp_obj_t o_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_repr_obj, mp_builtin_repr);
 
-STATIC mp_obj_t mp_builtin_round(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_round(size_t n_args, const mp_obj_t *args) {
     mp_obj_t o_in = args[0];
     if (MP_OBJ_IS_INT(o_in)) {
         return o_in;
@@ -490,7 +490,7 @@ STATIC mp_obj_t mp_builtin_round(mp_uint_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_round_obj, 1, 2, mp_builtin_round);
 
-STATIC mp_obj_t mp_builtin_sum(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_sum(size_t n_args, const mp_obj_t *args) {
     assert(1 <= n_args && n_args <= 2);
     mp_obj_t value;
     switch (n_args) {
@@ -506,7 +506,7 @@ STATIC mp_obj_t mp_builtin_sum(mp_uint_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_sum_obj, 1, 2, mp_builtin_sum);
 
-STATIC mp_obj_t mp_builtin_sorted(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+STATIC mp_obj_t mp_builtin_sorted(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     assert(n_args >= 1);
     if (n_args > 1) {
         nlr_raise(mp_obj_new_exception_msg(&mp_type_TypeError,
@@ -535,7 +535,7 @@ STATIC inline mp_obj_t mp_load_attr_default(mp_obj_t base, qstr attr, mp_obj_t d
     }
 }
 
-STATIC mp_obj_t mp_builtin_getattr(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_getattr(size_t n_args, const mp_obj_t *args) {
     mp_obj_t defval = MP_OBJ_NULL;
     if (n_args > 2) {
         defval = args[2];
diff --git a/py/modmath.c b/py/modmath.c
index cffd8cf491..6abf8ab3e9 100644
--- a/py/modmath.c
+++ b/py/modmath.c
@@ -152,7 +152,7 @@ MATH_FUN_1(lgamma, lgamma)
 // Function that takes a variable number of arguments
 
 // log(x[, base])
-STATIC mp_obj_t mp_math_log(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_math_log(size_t n_args, const mp_obj_t *args) {
     mp_float_t x = mp_obj_get_float(args[0]);
     if (x <= (mp_float_t)0.0) {
         math_error();
diff --git a/py/modmicropython.c b/py/modmicropython.c
index b5ab2e2653..ffc5413af3 100644
--- a/py/modmicropython.c
+++ b/py/modmicropython.c
@@ -53,7 +53,7 @@ STATIC mp_obj_t mp_micropython_mem_peak(void) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_0(mp_micropython_mem_peak_obj, mp_micropython_mem_peak);
 #endif
 
-mp_obj_t mp_micropython_mem_info(mp_uint_t n_args, const mp_obj_t *args) {
+mp_obj_t mp_micropython_mem_info(size_t n_args, const mp_obj_t *args) {
     (void)args;
 #if MICROPY_MEM_STATS
     mp_printf(&mp_plat_print, "mem: total=" UINT_FMT ", current=" UINT_FMT ", peak=" UINT_FMT "\n",
@@ -77,7 +77,7 @@ mp_obj_t mp_micropython_mem_info(mp_uint_t n_args, const mp_obj_t *args) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_micropython_mem_info_obj, 0, 1, mp_micropython_mem_info);
 
-STATIC mp_obj_t mp_micropython_qstr_info(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_micropython_qstr_info(size_t n_args, const mp_obj_t *args) {
     (void)args;
     size_t n_pool, n_qstr, n_str_data_bytes, n_total_bytes;
     qstr_pool_info(&n_pool, &n_qstr, &n_str_data_bytes, &n_total_bytes);
diff --git a/py/modstruct.c b/py/modstruct.c
index a52c5070fe..727a7ab006 100644
--- a/py/modstruct.c
+++ b/py/modstruct.c
@@ -165,7 +165,7 @@ STATIC mp_obj_t struct_unpack(mp_obj_t fmt_in, mp_obj_t data_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_2(struct_unpack_obj, struct_unpack);
 
-STATIC mp_obj_t struct_pack(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t struct_pack(size_t n_args, const mp_obj_t *args) {
     // TODO: "The arguments must match the values required by the format exactly."
     const char *fmt = mp_obj_str_get_str(args[0]);
     char fmt_type = get_fmt_type(&fmt);
diff --git a/py/modsys.c b/py/modsys.c
index 4bf7057c3d..3bc5c2bafc 100644
--- a/py/modsys.c
+++ b/py/modsys.c
@@ -93,7 +93,7 @@ STATIC const MP_DEFINE_STR_OBJ(platform_obj, MICROPY_PY_SYS_PLATFORM);
 /// \function exit([retval])
 /// Raise a `SystemExit` exception.  If an argument is given, it is the
 /// value given to `SystemExit`.
-STATIC mp_obj_t mp_sys_exit(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_sys_exit(size_t n_args, const mp_obj_t *args) {
     mp_obj_t exc;
     if (n_args == 0) {
         exc = mp_obj_new_exception(&mp_type_SystemExit);
@@ -104,7 +104,7 @@ STATIC mp_obj_t mp_sys_exit(mp_uint_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_sys_exit_obj, 0, 1, mp_sys_exit);
 
-STATIC mp_obj_t mp_sys_print_exception(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_sys_print_exception(size_t n_args, const mp_obj_t *args) {
     #if MICROPY_PY_IO
     void *stream_obj = &mp_sys_stdout_obj;
     if (n_args > 1) {
diff --git a/py/obj.h b/py/obj.h
index 88767bf1ae..52b8b4f8d4 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -395,8 +395,8 @@ typedef mp_obj_t (*mp_fun_0_t)(void);
 typedef mp_obj_t (*mp_fun_1_t)(mp_obj_t);
 typedef mp_obj_t (*mp_fun_2_t)(mp_obj_t, mp_obj_t);
 typedef mp_obj_t (*mp_fun_3_t)(mp_obj_t, mp_obj_t, mp_obj_t);
-typedef mp_obj_t (*mp_fun_var_t)(mp_uint_t n, const mp_obj_t *);
-typedef mp_obj_t (*mp_fun_kw_t)(mp_uint_t n, const mp_obj_t *, mp_map_t *);
+typedef mp_obj_t (*mp_fun_var_t)(size_t n, const mp_obj_t *);
+typedef mp_obj_t (*mp_fun_kw_t)(size_t n, const mp_obj_t *, mp_map_t *);
 
 typedef enum {
     PRINT_STR = 0,
@@ -725,7 +725,7 @@ mp_obj_t mp_obj_list_remove(mp_obj_t self_in, mp_obj_t value);
 void mp_obj_list_get(mp_obj_t self_in, mp_uint_t *len, mp_obj_t **items);
 void mp_obj_list_set_len(mp_obj_t self_in, mp_uint_t len);
 void mp_obj_list_store(mp_obj_t self_in, mp_obj_t index, mp_obj_t value);
-mp_obj_t mp_obj_list_sort(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
+mp_obj_t mp_obj_list_sort(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
 
 // dict
 typedef struct _mp_obj_dict_t {
diff --git a/py/objdict.c b/py/objdict.c
index 4010d9ce3f..cb4c602b99 100644
--- a/py/objdict.c
+++ b/py/objdict.c
@@ -36,7 +36,7 @@
 
 #define MP_OBJ_IS_DICT_TYPE(o) (MP_OBJ_IS_OBJ(o) && ((mp_obj_base_t*)MP_OBJ_TO_PTR(o))->type->make_new == dict_make_new)
 
-STATIC mp_obj_t dict_update(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
+STATIC mp_obj_t dict_update(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
 
 // This is a helper function to iterate through a dictionary.  The state of
 // the iteration is held in *cur and should be initialised with zero for the
@@ -240,7 +240,7 @@ STATIC mp_obj_t dict_copy(mp_obj_t self_in) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(dict_copy_obj, dict_copy);
 
 // this is a classmethod
-STATIC mp_obj_t dict_fromkeys(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t dict_fromkeys(size_t n_args, const mp_obj_t *args) {
     assert(2 <= n_args && n_args <= 3);
     mp_obj_t iter = mp_getiter(args[1]);
     mp_obj_t len = mp_obj_len_maybe(iter);
@@ -294,7 +294,7 @@ STATIC mp_obj_t dict_get_helper(mp_map_t *self, mp_obj_t key, mp_obj_t deflt, mp
     return value;
 }
 
-STATIC mp_obj_t dict_get(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t dict_get(size_t n_args, const mp_obj_t *args) {
     assert(2 <= n_args && n_args <= 3);
     assert(MP_OBJ_IS_DICT_TYPE(args[0]));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(args[0]);
@@ -306,7 +306,7 @@ STATIC mp_obj_t dict_get(mp_uint_t n_args, const mp_obj_t *args) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(dict_get_obj, 2, 3, dict_get);
 
-STATIC mp_obj_t dict_pop(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t dict_pop(size_t n_args, const mp_obj_t *args) {
     assert(2 <= n_args && n_args <= 3);
     assert(MP_OBJ_IS_DICT_TYPE(args[0]));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(args[0]);
@@ -319,7 +319,7 @@ STATIC mp_obj_t dict_pop(mp_uint_t n_args, const mp_obj_t *args) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(dict_pop_obj, 2, 3, dict_pop);
 
 
-STATIC mp_obj_t dict_setdefault(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t dict_setdefault(size_t n_args, const mp_obj_t *args) {
     assert(2 <= n_args && n_args <= 3);
     assert(MP_OBJ_IS_DICT_TYPE(args[0]));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(args[0]);
@@ -350,7 +350,7 @@ STATIC mp_obj_t dict_popitem(mp_obj_t self_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(dict_popitem_obj, dict_popitem);
 
-STATIC mp_obj_t dict_update(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+STATIC mp_obj_t dict_update(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     assert(MP_OBJ_IS_DICT_TYPE(args[0]));
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(args[0]);
 
diff --git a/py/objexcept.c b/py/objexcept.c
index 6e28a980bd..83aa5286c6 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -153,7 +153,7 @@ STATIC void exception_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     }
 }
 
-STATIC mp_obj_t exc___init__(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t exc___init__(size_t n_args, const mp_obj_t *args) {
     mp_obj_exception_t *self = MP_OBJ_TO_PTR(args[0]);
     mp_obj_t argst = mp_obj_new_tuple(n_args - 1, args + 1);
     self->args = MP_OBJ_TO_PTR(argst);
diff --git a/py/objgenerator.c b/py/objgenerator.c
index 91936f92f3..93df7ce13f 100644
--- a/py/objgenerator.c
+++ b/py/objgenerator.c
@@ -190,7 +190,7 @@ STATIC mp_obj_t gen_instance_send(mp_obj_t self_in, mp_obj_t send_value) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(gen_instance_send_obj, gen_instance_send);
 
 STATIC mp_obj_t gen_instance_close(mp_obj_t self_in);
-STATIC mp_obj_t gen_instance_throw(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t gen_instance_throw(size_t n_args, const mp_obj_t *args) {
     mp_obj_t exc = (n_args == 2) ? args[1] : args[2];
     exc = mp_make_raise_obj(exc);
 
diff --git a/py/objint.c b/py/objint.c
index 7ee7653cad..e548eb833e 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -381,7 +381,7 @@ mp_obj_t mp_obj_int_binary_op_extra_cases(mp_uint_t op, mp_obj_t lhs_in, mp_obj_
 }
 
 // this is a classmethod
-STATIC mp_obj_t int_from_bytes(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t int_from_bytes(size_t n_args, const mp_obj_t *args) {
     // TODO: Support long ints
     // TODO: Support byteorder param (assumes 'little' at the moment)
     // TODO: Support signed param (assumes signed=False at the moment)
@@ -403,7 +403,7 @@ STATIC mp_obj_t int_from_bytes(mp_uint_t n_args, const mp_obj_t *args) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(int_from_bytes_fun_obj, 2, 3, int_from_bytes);
 STATIC MP_DEFINE_CONST_CLASSMETHOD_OBJ(int_from_bytes_obj, MP_ROM_PTR(&int_from_bytes_fun_obj));
 
-STATIC mp_obj_t int_to_bytes(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t int_to_bytes(size_t n_args, const mp_obj_t *args) {
     // TODO: Support byteorder param (assumes 'little')
     // TODO: Support signed param (assumes signed=False)
     (void)n_args;
diff --git a/py/objlist.c b/py/objlist.c
index 059fec1b25..3fd38e81d9 100644
--- a/py/objlist.c
+++ b/py/objlist.c
@@ -36,7 +36,7 @@
 STATIC mp_obj_t mp_obj_new_list_iterator(mp_obj_t list, mp_uint_t cur);
 STATIC mp_obj_list_t *list_new(mp_uint_t n);
 STATIC mp_obj_t list_extend(mp_obj_t self_in, mp_obj_t arg_in);
-STATIC mp_obj_t list_pop(mp_uint_t n_args, const mp_obj_t *args);
+STATIC mp_obj_t list_pop(size_t n_args, const mp_obj_t *args);
 
 // TODO: Move to mpconfig.h
 #define LIST_MIN_ALLOC 4
@@ -262,7 +262,7 @@ STATIC mp_obj_t list_extend(mp_obj_t self_in, mp_obj_t arg_in) {
     return mp_const_none; // return None, as per CPython
 }
 
-STATIC mp_obj_t list_pop(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t list_pop(size_t n_args, const mp_obj_t *args) {
     assert(1 <= n_args && n_args <= 2);
     assert(MP_OBJ_IS_TYPE(args[0], &mp_type_list));
     mp_obj_list_t *self = MP_OBJ_TO_PTR(args[0]);
@@ -311,7 +311,7 @@ STATIC void mp_quicksort(mp_obj_t *head, mp_obj_t *tail, mp_obj_t key_fn, mp_obj
 }
 
 // TODO Python defines sort to be stable but ours is not
-mp_obj_t mp_obj_list_sort(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+mp_obj_t mp_obj_list_sort(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_key, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} },
         { MP_QSTR_reverse, MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
@@ -355,7 +355,7 @@ STATIC mp_obj_t list_count(mp_obj_t self_in, mp_obj_t value) {
     return mp_seq_count_obj(self->items, self->len, value);
 }
 
-STATIC mp_obj_t list_index(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t list_index(size_t n_args, const mp_obj_t *args) {
     assert(2 <= n_args && n_args <= 4);
     assert(MP_OBJ_IS_TYPE(args[0], &mp_type_list));
     mp_obj_list_t *self = MP_OBJ_TO_PTR(args[0]);
diff --git a/py/objset.c b/py/objset.c
index 6ac9c580ab..c83212c433 100644
--- a/py/objset.c
+++ b/py/objset.c
@@ -223,7 +223,7 @@ STATIC mp_obj_t set_discard(mp_obj_t self_in, mp_obj_t item) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(set_discard_obj, set_discard);
 
-STATIC mp_obj_t set_diff_int(mp_uint_t n_args, const mp_obj_t *args, bool update) {
+STATIC mp_obj_t set_diff_int(size_t n_args, const mp_obj_t *args, bool update) {
     assert(n_args > 0);
 
     mp_obj_t self;
@@ -253,12 +253,12 @@ STATIC mp_obj_t set_diff_int(mp_uint_t n_args, const mp_obj_t *args, bool update
     return self;
 }
 
-STATIC mp_obj_t set_diff(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t set_diff(size_t n_args, const mp_obj_t *args) {
     return set_diff_int(n_args, args, false);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR(set_diff_obj, 1, set_diff);
 
-STATIC mp_obj_t set_diff_update(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t set_diff_update(size_t n_args, const mp_obj_t *args) {
     set_diff_int(n_args, args, true);
     return mp_const_none;
 }
@@ -442,7 +442,7 @@ STATIC void set_update_int(mp_obj_set_t *self, mp_obj_t other_in) {
     }
 }
 
-STATIC mp_obj_t set_update(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t set_update(size_t n_args, const mp_obj_t *args) {
     assert(n_args > 0);
 
     for (mp_uint_t i = 1; i < n_args; i++) {
diff --git a/py/objstr.c b/py/objstr.c
index 55c7cdd5f7..a76ff0d736 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -546,12 +546,12 @@ STATIC inline mp_obj_t str_split_internal(mp_uint_t n_args, const mp_obj_t *args
     return res;
 }
 
-mp_obj_t mp_obj_str_split(mp_uint_t n_args, const mp_obj_t *args) {
+mp_obj_t mp_obj_str_split(size_t n_args, const mp_obj_t *args) {
     return str_split_internal(n_args, args, SPLIT);
 }
 
 #if MICROPY_PY_BUILTINS_STR_SPLITLINES
-STATIC mp_obj_t str_splitlines(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+STATIC mp_obj_t str_splitlines(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_keepends, MP_ARG_BOOL, {.u_bool = false} },
     };
@@ -565,7 +565,7 @@ STATIC mp_obj_t str_splitlines(mp_uint_t n_args, const mp_obj_t *pos_args, mp_ma
 }
 #endif
 
-STATIC mp_obj_t str_rsplit(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_rsplit(size_t n_args, const mp_obj_t *args) {
     if (n_args < 3) {
         // If we don't have split limit, it doesn't matter from which side
         // we split.
@@ -667,24 +667,24 @@ STATIC mp_obj_t str_finder(mp_uint_t n_args, const mp_obj_t *args, mp_int_t dire
     }
 }
 
-STATIC mp_obj_t str_find(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_find(size_t n_args, const mp_obj_t *args) {
     return str_finder(n_args, args, 1, false);
 }
 
-STATIC mp_obj_t str_rfind(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_rfind(size_t n_args, const mp_obj_t *args) {
     return str_finder(n_args, args, -1, false);
 }
 
-STATIC mp_obj_t str_index(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_index(size_t n_args, const mp_obj_t *args) {
     return str_finder(n_args, args, 1, true);
 }
 
-STATIC mp_obj_t str_rindex(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_rindex(size_t n_args, const mp_obj_t *args) {
     return str_finder(n_args, args, -1, true);
 }
 
 // TODO: (Much) more variety in args
-STATIC mp_obj_t str_startswith(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_startswith(size_t n_args, const mp_obj_t *args) {
     const mp_obj_type_t *self_type = mp_obj_get_type(args[0]);
     GET_STR_DATA_LEN(args[0], str, str_len);
     GET_STR_DATA_LEN(args[1], prefix, prefix_len);
@@ -698,7 +698,7 @@ STATIC mp_obj_t str_startswith(mp_uint_t n_args, const mp_obj_t *args) {
     return mp_obj_new_bool(memcmp(start, prefix, prefix_len) == 0);
 }
 
-STATIC mp_obj_t str_endswith(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_endswith(size_t n_args, const mp_obj_t *args) {
     GET_STR_DATA_LEN(args[0], str, str_len);
     GET_STR_DATA_LEN(args[1], suffix, suffix_len);
     if (n_args > 2) {
@@ -785,15 +785,15 @@ STATIC mp_obj_t str_uni_strip(int type, mp_uint_t n_args, const mp_obj_t *args)
     return mp_obj_new_str_of_type(self_type, orig_str + first_good_char_pos, stripped_len);
 }
 
-STATIC mp_obj_t str_strip(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_strip(size_t n_args, const mp_obj_t *args) {
     return str_uni_strip(STRIP, n_args, args);
 }
 
-STATIC mp_obj_t str_lstrip(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_lstrip(size_t n_args, const mp_obj_t *args) {
     return str_uni_strip(LSTRIP, n_args, args);
 }
 
-STATIC mp_obj_t str_rstrip(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_rstrip(size_t n_args, const mp_obj_t *args) {
     return str_uni_strip(RSTRIP, n_args, args);
 }
 
@@ -845,7 +845,7 @@ STATIC NORETURN void terse_str_format_value_error(void) {
     nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "bad format string"));
 }
 
-mp_obj_t mp_obj_str_format(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+mp_obj_t mp_obj_str_format(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     assert(MP_OBJ_IS_STR_OR_BYTES(args[0]));
 
     GET_STR_DATA_LEN(args[0], str, len);
@@ -1486,7 +1486,7 @@ not_enough_args:
 
 // The implementation is optimized, returning the original string if there's
 // nothing to replace.
-STATIC mp_obj_t str_replace(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_replace(size_t n_args, const mp_obj_t *args) {
     assert(MP_OBJ_IS_STR_OR_BYTES(args[0]));
 
     mp_int_t max_rep = -1;
@@ -1591,7 +1591,7 @@ STATIC mp_obj_t str_replace(mp_uint_t n_args, const mp_obj_t *args) {
     return mp_obj_new_str_from_vstr(self_type, &vstr);
 }
 
-STATIC mp_obj_t str_count(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_count(size_t n_args, const mp_obj_t *args) {
     const mp_obj_type_t *self_type = mp_obj_get_type(args[0]);
     assert(2 <= n_args && n_args <= 4);
     assert(MP_OBJ_IS_STR_OR_BYTES(args[0]));
@@ -1759,7 +1759,7 @@ STATIC mp_obj_t str_islower(mp_obj_t self_in) {
 // These methods are superfluous in the presense of str() and bytes()
 // constructors.
 // TODO: should accept kwargs too
-STATIC mp_obj_t bytes_decode(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t bytes_decode(size_t n_args, const mp_obj_t *args) {
     mp_obj_t new_args[2];
     if (n_args == 1) {
         new_args[0] = args[0];
@@ -1771,7 +1771,7 @@ STATIC mp_obj_t bytes_decode(mp_uint_t n_args, const mp_obj_t *args) {
 }
 
 // TODO: should accept kwargs too
-STATIC mp_obj_t str_encode(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t str_encode(size_t n_args, const mp_obj_t *args) {
     mp_obj_t new_args[2];
     if (n_args == 1) {
         new_args[0] = args[0];
diff --git a/py/objstr.h b/py/objstr.h
index d9327b1ab8..1cfb195038 100644
--- a/py/objstr.h
+++ b/py/objstr.h
@@ -62,8 +62,8 @@ const byte *mp_obj_str_get_data_no_check(mp_obj_t self_in, size_t *len);
 
 mp_obj_t mp_obj_str_make_new(mp_obj_t type_in, size_t n_args, size_t n_kw, const mp_obj_t *args);
 void mp_str_print_json(const mp_print_t *print, const byte *str_data, size_t str_len);
-mp_obj_t mp_obj_str_format(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
-mp_obj_t mp_obj_str_split(mp_uint_t n_args, const mp_obj_t *args);
+mp_obj_t mp_obj_str_format(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
+mp_obj_t mp_obj_str_split(size_t n_args, const mp_obj_t *args);
 mp_obj_t mp_obj_new_str_of_type(const mp_obj_type_t *type, const byte* data, size_t len);
 
 mp_obj_t mp_obj_str_binary_op(mp_uint_t op, mp_obj_t lhs_in, mp_obj_t rhs_in);
diff --git a/py/objstringio.c b/py/objstringio.c
index d046cdd80d..357320cd2f 100644
--- a/py/objstringio.c
+++ b/py/objstringio.c
@@ -114,7 +114,7 @@ STATIC mp_obj_t stringio_close(mp_obj_t self_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(stringio_close_obj, stringio_close);
 
-STATIC mp_obj_t stringio___exit__(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t stringio___exit__(size_t n_args, const mp_obj_t *args) {
     (void)n_args;
     return stringio_close(args[0]);
 }
diff --git a/py/objtuple.c b/py/objtuple.c
index 8337b67042..86720ed374 100644
--- a/py/objtuple.c
+++ b/py/objtuple.c
@@ -208,7 +208,7 @@ STATIC mp_obj_t tuple_count(mp_obj_t self_in, mp_obj_t value) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(tuple_count_obj, tuple_count);
 
-STATIC mp_obj_t tuple_index(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t tuple_index(size_t n_args, const mp_obj_t *args) {
     assert(MP_OBJ_IS_TYPE(args[0], &mp_type_tuple));
     mp_obj_tuple_t *self = MP_OBJ_TO_PTR(args[0]);
     return mp_seq_index_obj(self->items, self->len, n_args, args);
diff --git a/py/stream.c b/py/stream.c
index d29db621bc..82bdffe2b2 100644
--- a/py/stream.c
+++ b/py/stream.c
@@ -62,7 +62,7 @@ const mp_stream_p_t *mp_get_stream_raise(mp_obj_t self_in, int flags) {
     return stream_p;
 }
 
-STATIC mp_obj_t stream_read(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t stream_read(size_t n_args, const mp_obj_t *args) {
     const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
 
     // What to do if sz < -1?  Python docs don't specify this case.
@@ -214,7 +214,7 @@ STATIC mp_obj_t stream_write_method(mp_obj_t self_in, mp_obj_t arg) {
     return mp_stream_write(self_in, bufinfo.buf, bufinfo.len);
 }
 
-STATIC mp_obj_t stream_readinto(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t stream_readinto(size_t n_args, const mp_obj_t *args) {
     const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(args[1], &bufinfo, MP_BUFFER_WRITE);
@@ -287,7 +287,7 @@ STATIC mp_obj_t stream_readall(mp_obj_t self_in) {
 }
 
 // Unbuffered, inefficient implementation of readline() for raw I/O files.
-STATIC mp_obj_t stream_unbuffered_readline(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t stream_unbuffered_readline(size_t n_args, const mp_obj_t *args) {
     const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_READ);
 
     mp_int_t max_size = -1;
@@ -365,7 +365,7 @@ mp_obj_t mp_stream_unbuffered_iter(mp_obj_t self) {
     return MP_OBJ_STOP_ITERATION;
 }
 
-STATIC mp_obj_t stream_seek(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t stream_seek(size_t n_args, const mp_obj_t *args) {
     const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_IOCTL);
 
     struct mp_stream_seek_t seek_s;
diff --git a/qemu-arm/main.c b/qemu-arm/main.c
index e0f9a10ae6..f295475234 100644
--- a/qemu-arm/main.c
+++ b/qemu-arm/main.c
@@ -52,7 +52,7 @@ mp_import_stat_t mp_import_stat(const char *path) {
     return MP_IMPORT_STAT_NO_EXIST;
 }
 
-mp_obj_t mp_builtin_open(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);
diff --git a/qemu-arm/test_main.c b/qemu-arm/test_main.c
index f678946d49..a98e275cee 100644
--- a/qemu-arm/test_main.c
+++ b/qemu-arm/test_main.c
@@ -82,7 +82,7 @@ mp_import_stat_t mp_import_stat(const char *path) {
     return MP_IMPORT_STAT_NO_EXIST;
 }
 
-mp_obj_t mp_builtin_open(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);
diff --git a/unix/file.c b/unix/file.c
index 751d62fd51..2d3eb7b5a2 100644
--- a/unix/file.c
+++ b/unix/file.c
@@ -130,7 +130,7 @@ STATIC mp_obj_t fdfile_close(mp_obj_t self_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(fdfile_close_obj, fdfile_close);
 
-STATIC mp_obj_t fdfile___exit__(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t fdfile___exit__(size_t n_args, const mp_obj_t *args) {
     (void)n_args;
     return fdfile_close(args[0]);
 }
@@ -264,7 +264,7 @@ const mp_obj_type_t mp_type_textio = {
 };
 
 // Factory function for I/O stream classes
-mp_obj_t mp_builtin_open(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
     // TODO: analyze buffering args and instantiate appropriate type
     mp_arg_val_t arg_vals[FILE_OPEN_NUM_ARGS];
     mp_arg_parse_all(n_args, args, kwargs, FILE_OPEN_NUM_ARGS, file_open_args, arg_vals);
diff --git a/unix/input.c b/unix/input.c
index 66b3314c98..15ee60e750 100644
--- a/unix/input.c
+++ b/unix/input.c
@@ -158,7 +158,7 @@ void prompt_write_history(void) {
 #endif
 }
 
-STATIC mp_obj_t mp_builtin_input(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mp_builtin_input(size_t n_args, const mp_obj_t *args) {
     if (n_args == 1) {
         mp_obj_print(args[0], PRINT_STR);
     }
diff --git a/unix/modffi.c b/unix/modffi.c
index be12974979..337f7a7b7c 100644
--- a/unix/modffi.c
+++ b/unix/modffi.c
@@ -208,7 +208,7 @@ STATIC mp_obj_t make_func(mp_obj_t rettype_in, void *func, mp_obj_t argtypes_in)
     return MP_OBJ_FROM_PTR(o);
 }
 
-STATIC mp_obj_t ffimod_func(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t ffimod_func(size_t n_args, const mp_obj_t *args) {
     (void)n_args; // always 4
     mp_obj_ffimod_t *self = MP_OBJ_TO_PTR(args[0]);
     const char *symname = mp_obj_str_get_str(args[2]);
@@ -477,7 +477,7 @@ STATIC const mp_obj_type_t opaque_type = {
 };
 */
 
-STATIC mp_obj_t mod_ffi_open(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_ffi_open(size_t n_args, const mp_obj_t *args) {
     return ffimod_make_new((mp_obj_t)&ffimod_type, n_args, 0, args);
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_ffi_open_obj, 1, 2, mod_ffi_open);
diff --git a/unix/modos.c b/unix/modos.c
index ee61ad3f38..f6b3f0b97b 100644
--- a/unix/modos.c
+++ b/unix/modos.c
@@ -193,7 +193,7 @@ STATIC mp_obj_t listdir_next(mp_obj_t self_in) {
     return MP_OBJ_FROM_PTR(t);
 }
 
-STATIC mp_obj_t mod_os_ilistdir(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_os_ilistdir(size_t n_args, const mp_obj_t *args) {
     const char *path = ".";
     if (n_args > 0) {
         path = mp_obj_str_get_str(args[0]);
@@ -206,7 +206,7 @@ STATIC mp_obj_t mod_os_ilistdir(mp_uint_t n_args, const mp_obj_t *args) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_os_ilistdir_obj, 0, 1, mod_os_ilistdir);
 
-STATIC mp_obj_t mod_os_errno(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_os_errno(size_t n_args, const mp_obj_t *args) {
     if (n_args == 0) {
         return MP_OBJ_NEW_SMALL_INT(errno);
     }
diff --git a/unix/modsocket.c b/unix/modsocket.c
index 0857d05733..a9bb2e09ce 100644
--- a/unix/modsocket.c
+++ b/unix/modsocket.c
@@ -171,7 +171,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(socket_accept_obj, socket_accept);
 // Note: besides flag param, this differs from read() in that
 // this does not swallow blocking errors (EAGAIN, EWOULDBLOCK) -
 // these would be thrown as exceptions.
-STATIC mp_obj_t socket_recv(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t socket_recv(size_t n_args, const mp_obj_t *args) {
     mp_obj_socket_t *self = MP_OBJ_TO_PTR(args[0]);
     int sz = MP_OBJ_SMALL_INT_VALUE(args[1]);
     int flags = 0;
@@ -190,7 +190,7 @@ STATIC mp_obj_t socket_recv(mp_uint_t n_args, const mp_obj_t *args) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(socket_recv_obj, 2, 3, socket_recv);
 
-STATIC mp_obj_t socket_recvfrom(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t socket_recvfrom(size_t n_args, const mp_obj_t *args) {
     mp_obj_socket_t *self = MP_OBJ_TO_PTR(args[0]);
     int sz = MP_OBJ_SMALL_INT_VALUE(args[1]);
     int flags = 0;
@@ -220,7 +220,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(socket_recvfrom_obj, 2, 3, socket_rec
 // Note: besides flag param, this differs from write() in that
 // this does not swallow blocking errors (EAGAIN, EWOULDBLOCK) -
 // these would be thrown as exceptions.
-STATIC mp_obj_t socket_send(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t socket_send(size_t n_args, const mp_obj_t *args) {
     mp_obj_socket_t *self = MP_OBJ_TO_PTR(args[0]);
     int flags = 0;
 
@@ -237,7 +237,7 @@ STATIC mp_obj_t socket_send(mp_uint_t n_args, const mp_obj_t *args) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(socket_send_obj, 2, 3, socket_send);
 
-STATIC mp_obj_t socket_sendto(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t socket_sendto(size_t n_args, const mp_obj_t *args) {
     mp_obj_socket_t *self = MP_OBJ_TO_PTR(args[0]);
     int flags = 0;
 
@@ -258,7 +258,7 @@ STATIC mp_obj_t socket_sendto(mp_uint_t n_args, const mp_obj_t *args) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(socket_sendto_obj, 3, 4, socket_sendto);
 
-STATIC mp_obj_t socket_setsockopt(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t socket_setsockopt(size_t n_args, const mp_obj_t *args) {
     (void)n_args; // always 4
     mp_obj_socket_t *self = MP_OBJ_TO_PTR(args[0]);
     int level = MP_OBJ_SMALL_INT_VALUE(args[1]);
@@ -299,7 +299,7 @@ STATIC mp_obj_t socket_setblocking(mp_obj_t self_in, mp_obj_t flag_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(socket_setblocking_obj, socket_setblocking);
 
-STATIC mp_obj_t socket_makefile(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t socket_makefile(size_t n_args, const mp_obj_t *args) {
     // TODO: CPython explicitly says that closing returned object doesn't close
     // the original socket (Python2 at all says that fd is dup()ed). But we
     // save on the bloat.
@@ -421,7 +421,7 @@ STATIC mp_obj_t mod_socket_inet_pton(mp_obj_t family_in, mp_obj_t addr_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_socket_inet_pton_obj, mod_socket_inet_pton);
 
-STATIC mp_obj_t mod_socket_getaddrinfo(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_socket_getaddrinfo(size_t n_args, const mp_obj_t *args) {
     // TODO: Implement all args
     assert(n_args >= 2 && n_args <= 4);
     assert(MP_OBJ_IS_STR(args[0]));
diff --git a/unix/modtime.c b/unix/modtime.c
index 32a4a6c71f..d3b780790c 100644
--- a/unix/modtime.c
+++ b/unix/modtime.c
@@ -154,7 +154,7 @@ STATIC mp_obj_t mod_time_sleep_us(mp_obj_t arg) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_time_sleep_us_obj, mod_time_sleep_us);
 
-STATIC mp_obj_t mod_time_strftime(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t mod_time_strftime(size_t n_args, const mp_obj_t *args) {
     time_t t;
     if (n_args == 1) {
         t = time(NULL);
diff --git a/unix/moduselect.c b/unix/moduselect.c
index 7e0ec049f1..13cb3f1fa8 100644
--- a/unix/moduselect.c
+++ b/unix/moduselect.c
@@ -52,7 +52,7 @@ typedef struct _mp_obj_poll_t {
 } mp_obj_poll_t;
 
 /// \method register(obj[, eventmask])
-STATIC mp_obj_t poll_register(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t poll_register(size_t n_args, const mp_obj_t *args) {
     mp_obj_poll_t *self = MP_OBJ_TO_PTR(args[0]);
     int fd = mp_obj_get_int(args[1]);
     mp_uint_t flags;
@@ -129,7 +129,7 @@ MP_DEFINE_CONST_FUN_OBJ_3(poll_modify_obj, poll_modify);
 
 /// \method poll([timeout])
 /// Timeout is in milliseconds.
-STATIC mp_obj_t poll_poll(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t poll_poll(size_t n_args, const mp_obj_t *args) {
     mp_obj_poll_t *self = MP_OBJ_TO_PTR(args[0]);
 
     // work out timeout (it's given already in ms)
@@ -186,7 +186,7 @@ STATIC const mp_obj_type_t mp_type_poll = {
     .locals_dict = (void*)&poll_locals_dict,
 };
 
-STATIC mp_obj_t select_poll(mp_uint_t n_args, const mp_obj_t *args) {
+STATIC mp_obj_t select_poll(size_t n_args, const mp_obj_t *args) {
     int alloc = 4;
     if (n_args > 0) {
         alloc = mp_obj_get_int(args[0]);