diff --git a/docs/library/ujson.rst b/docs/library/ujson.rst
index 5668eb21a8..65ed1867e6 100644
--- a/docs/library/ujson.rst
+++ b/docs/library/ujson.rst
@@ -12,14 +12,20 @@ data format.
 Functions
 ---------
 
-.. function:: dump(obj, stream)
+.. function:: dump(obj, stream, separators=None)
 
    Serialise *obj* to a JSON string, writing it to the given *stream*.
 
-.. function:: dumps(obj)
+   If specified, separators should be an ``(item_separator, key_separator)``
+   tuple. The default is ``(', ', ': ')``. To get the most compact JSON
+   representation, you should specify ``(',', ':')`` to eliminate whitespace.
+
+.. function:: dumps(obj, separators=None)
 
    Return *obj* represented as a JSON string.
 
+   The arguments have the same meaning as in `dump`.
+
 .. function:: load(stream)
 
    Parse the given *stream*, interpreting it as a JSON string and
diff --git a/extmod/modujson.c b/extmod/modujson.c
index 8dff673580..e5bfb0d966 100644
--- a/extmod/modujson.c
+++ b/extmod/modujson.c
@@ -34,6 +34,62 @@
 
 #if MICROPY_PY_UJSON
 
+#if MICROPY_PY_UJSON_SEPARATORS
+
+enum {
+    DUMP_MODE_TO_STRING = 1,
+    DUMP_MODE_TO_STREAM = 2,
+};
+
+STATIC mp_obj_t mod_ujson_dump_helper(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args, unsigned int mode) {
+    enum { ARG_separators };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_separators, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
+    };
+
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args - mode, pos_args + mode, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    mp_print_ext_t print_ext;
+
+    if (args[ARG_separators].u_obj == mp_const_none) {
+        print_ext.item_separator = ", ";
+        print_ext.key_separator = ": ";
+    } else {
+        mp_obj_t *items;
+        mp_obj_get_array_fixed_n(args[ARG_separators].u_obj, 2, &items);
+        print_ext.item_separator = mp_obj_str_get_str(items[0]);
+        print_ext.key_separator = mp_obj_str_get_str(items[1]);
+    }
+
+    if (mode == DUMP_MODE_TO_STRING) {
+        // dumps(obj)
+        vstr_t vstr;
+        vstr_init_print(&vstr, 8, &print_ext.base);
+        mp_obj_print_helper(&print_ext.base, pos_args[0], PRINT_JSON);
+        return mp_obj_new_str_from_vstr(&mp_type_str, &vstr);
+    } else {
+        // dump(obj, stream)
+        print_ext.base.data = MP_OBJ_TO_PTR(pos_args[1]);
+        print_ext.base.print_strn = mp_stream_write_adaptor;
+        mp_get_stream_raise(pos_args[1], MP_STREAM_OP_WRITE);
+        mp_obj_print_helper(&print_ext.base, pos_args[0], PRINT_JSON);
+        return mp_const_none;
+    }
+}
+
+STATIC mp_obj_t mod_ujson_dump(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    return mod_ujson_dump_helper(n_args, pos_args, kw_args, DUMP_MODE_TO_STREAM);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_KW(mod_ujson_dump_obj, 2, mod_ujson_dump);
+
+STATIC mp_obj_t mod_ujson_dumps(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    return mod_ujson_dump_helper(n_args, pos_args, kw_args, DUMP_MODE_TO_STRING);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_KW(mod_ujson_dumps_obj, 1, mod_ujson_dumps);
+
+#else
+
 STATIC mp_obj_t mod_ujson_dump(mp_obj_t obj, mp_obj_t stream) {
     mp_get_stream_raise(stream, MP_STREAM_OP_WRITE);
     mp_print_t print = {MP_OBJ_TO_PTR(stream), mp_stream_write_adaptor};
@@ -51,6 +107,8 @@ STATIC mp_obj_t mod_ujson_dumps(mp_obj_t obj) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_ujson_dumps_obj, mod_ujson_dumps);
 
+#endif
+
 // The function below implements a simple non-recursive JSON parser.
 //
 // The JSON specification is at http://www.ietf.org/rfc/rfc4627.txt
diff --git a/py/mpconfig.h b/py/mpconfig.h
index f67e11cd4b..a91c39b018 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -1380,6 +1380,11 @@ typedef double mp_float_t;
 #define MICROPY_PY_UJSON (0)
 #endif
 
+// Whether to support the "separators" argument to dump, dumps
+#ifndef MICROPY_PY_UJSON_SEPARATORS
+#define MICROPY_PY_UJSON_SEPARATORS (1)
+#endif
+
 #ifndef MICROPY_PY_URE
 #define MICROPY_PY_URE (0)
 #endif
diff --git a/py/mpprint.h b/py/mpprint.h
index aef9015deb..0dff9a770a 100644
--- a/py/mpprint.h
+++ b/py/mpprint.h
@@ -52,6 +52,14 @@ typedef struct _mp_print_t {
     mp_print_strn_t print_strn;
 } mp_print_t;
 
+typedef struct _mp_print_ext_t {
+    mp_print_t base;
+    const char *item_separator;
+    const char *key_separator;
+}mp_print_ext_t;
+
+#define MP_PRINT_GET_EXT(print) ((mp_print_ext_t *)print)
+
 // All (non-debug) prints go through one of the two interfaces below.
 // 1) Wrapper for platform print function, which wraps MP_PLAT_PRINT_STRN.
 extern const mp_print_t mp_plat_print;
diff --git a/py/objdict.c b/py/objdict.c
index 63e5381c66..ed4376aa4f 100644
--- a/py/objdict.c
+++ b/py/objdict.c
@@ -69,8 +69,15 @@ STATIC mp_map_elem_t *dict_iter_next(mp_obj_dict_t *dict, size_t *cur) {
 STATIC void dict_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
     mp_obj_dict_t *self = MP_OBJ_TO_PTR(self_in);
     bool first = true;
+    const char *item_separator = ", ";
+    const char *key_separator = ": ";
     if (!(MICROPY_PY_UJSON && kind == PRINT_JSON)) {
         kind = PRINT_REPR;
+    } else {
+        #if MICROPY_PY_UJSON_SEPARATORS
+        item_separator = MP_PRINT_GET_EXT(print)->item_separator;
+        key_separator = MP_PRINT_GET_EXT(print)->key_separator;
+        #endif
     }
     if (MICROPY_PY_COLLECTIONS_ORDEREDDICT && self->base.type != &mp_type_dict && kind != PRINT_JSON) {
         mp_printf(print, "%q(", self->base.type->name);
@@ -80,7 +87,7 @@ STATIC void dict_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_
     mp_map_elem_t *next = NULL;
     while ((next = dict_iter_next(self, &cur)) != NULL) {
         if (!first) {
-            mp_print_str(print, ", ");
+            mp_print_str(print, item_separator);
         }
         first = false;
         bool add_quote = MICROPY_PY_UJSON && kind == PRINT_JSON && !mp_obj_is_str_or_bytes(next->key);
@@ -91,7 +98,7 @@ STATIC void dict_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_
         if (add_quote) {
             mp_print_str(print, "\"");
         }
-        mp_print_str(print, ": ");
+        mp_print_str(print, key_separator);
         mp_obj_print_helper(print, next->value, kind);
     }
     mp_print_str(print, "}");
diff --git a/py/objlist.c b/py/objlist.c
index 8c989facc0..f431e273df 100644
--- a/py/objlist.c
+++ b/py/objlist.c
@@ -44,13 +44,18 @@ STATIC mp_obj_t list_pop(size_t n_args, const mp_obj_t *args);
 
 STATIC void list_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind) {
     mp_obj_list_t *o = MP_OBJ_TO_PTR(o_in);
+    const char *item_separator = ", ";
     if (!(MICROPY_PY_UJSON && kind == PRINT_JSON)) {
         kind = PRINT_REPR;
+    } else {
+        #if MICROPY_PY_UJSON_SEPARATORS
+        item_separator = MP_PRINT_GET_EXT(print)->item_separator;
+        #endif
     }
     mp_print_str(print, "[");
     for (size_t i = 0; i < o->len; i++) {
         if (i > 0) {
-            mp_print_str(print, ", ");
+            mp_print_str(print, item_separator);
         }
         mp_obj_print_helper(print, o->items[i], kind);
     }
diff --git a/py/objtuple.c b/py/objtuple.c
index 07a560ac08..67d7bc356f 100644
--- a/py/objtuple.c
+++ b/py/objtuple.c
@@ -39,15 +39,19 @@
 
 void mp_obj_tuple_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_t kind) {
     mp_obj_tuple_t *o = MP_OBJ_TO_PTR(o_in);
+    const char *item_separator = ", ";
     if (MICROPY_PY_UJSON && kind == PRINT_JSON) {
         mp_print_str(print, "[");
+        #if MICROPY_PY_UJSON_SEPARATORS
+        item_separator = MP_PRINT_GET_EXT(print)->item_separator;
+        #endif
     } else {
         mp_print_str(print, "(");
         kind = PRINT_REPR;
     }
     for (size_t i = 0; i < o->len; i++) {
         if (i > 0) {
-            mp_print_str(print, ", ");
+            mp_print_str(print, item_separator);
         }
         mp_obj_print_helper(print, o->items[i], kind);
     }