diff --git a/extmod/modbtree.c b/extmod/modbtree.c
index 27f700eea4..127dd71a39 100644
--- a/extmod/modbtree.c
+++ b/extmod/modbtree.c
@@ -97,12 +97,8 @@ STATIC mp_obj_t btree_put(size_t n_args, const mp_obj_t *args) {
     (void)n_args;
     mp_obj_btree_t *self = MP_OBJ_TO_PTR(args[0]);
     DBT key, val;
-    // Different ports may have different type sizes
-    mp_uint_t v;
-    key.data = (void*)mp_obj_str_get_data(args[1], &v);
-    key.size = v;
-    val.data = (void*)mp_obj_str_get_data(args[2], &v);
-    val.size = v;
+    key.data = (void*)mp_obj_str_get_data(args[1], &key.size);
+    val.data = (void*)mp_obj_str_get_data(args[2], &val.size);
     return MP_OBJ_NEW_SMALL_INT(__bt_put(self->db, &key, &val, 0));
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(btree_put_obj, 3, 4, btree_put);
@@ -110,10 +106,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(btree_put_obj, 3, 4, btree_put);
 STATIC mp_obj_t btree_get(size_t n_args, const mp_obj_t *args) {
     mp_obj_btree_t *self = MP_OBJ_TO_PTR(args[0]);
     DBT key, val;
-    // Different ports may have different type sizes
-    mp_uint_t v;
-    key.data = (void*)mp_obj_str_get_data(args[1], &v);
-    key.size = v;
+    key.data = (void*)mp_obj_str_get_data(args[1], &key.size);
     int res = __bt_get(self->db, &key, &val, 0);
     if (res == RET_SPECIAL) {
         if (n_args > 2) {
@@ -132,10 +125,7 @@ STATIC mp_obj_t btree_seq(size_t n_args, const mp_obj_t *args) {
     int flags = MP_OBJ_SMALL_INT_VALUE(args[1]);
     DBT key, val;
     if (n_args > 2) {
-        // Different ports may have different type sizes
-        mp_uint_t v;
-        key.data = (void*)mp_obj_str_get_data(args[2], &v);
-        key.size = v;
+        key.data = (void*)mp_obj_str_get_data(args[2], &key.size);
     }
 
     int res = __bt_seq(self->db, &key, &val, flags);
@@ -206,14 +196,11 @@ STATIC mp_obj_t btree_iternext(mp_obj_t self_in) {
     mp_obj_btree_t *self = MP_OBJ_TO_PTR(self_in);
     DBT key, val;
     int res;
-    // Different ports may have different type sizes
-    mp_uint_t v;
     bool desc = self->flags & FLAG_DESC;
     if (self->start_key != MP_OBJ_NULL) {
         int flags = R_FIRST;
         if (self->start_key != mp_const_none) {
-            key.data = (void*)mp_obj_str_get_data(self->start_key, &v);
-            key.size = v;
+            key.data = (void*)mp_obj_str_get_data(self->start_key, &key.size);
             flags = R_CURSOR;
         } else if (desc) {
             flags = R_LAST;
@@ -231,8 +218,7 @@ STATIC mp_obj_t btree_iternext(mp_obj_t self_in) {
 
     if (self->end_key != mp_const_none) {
         DBT end_key;
-        end_key.data = (void*)mp_obj_str_get_data(self->end_key, &v);
-        end_key.size = v;
+        end_key.data = (void*)mp_obj_str_get_data(self->end_key, &end_key.size);
         BTREE *t = self->db->internal;
         int cmp = t->bt_cmp(&key, &end_key);
         if (desc) {
@@ -264,13 +250,10 @@ STATIC mp_obj_t btree_iternext(mp_obj_t self_in) {
 
 STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     mp_obj_btree_t *self = MP_OBJ_TO_PTR(self_in);
-    // Different ports may have different type sizes
-    mp_uint_t v;
     if (value == MP_OBJ_NULL) {
         // delete
         DBT key;
-        key.data = (void*)mp_obj_str_get_data(index, &v);
-        key.size = v;
+        key.data = (void*)mp_obj_str_get_data(index, &key.size);
         int res = __bt_delete(self->db, &key, 0);
         if (res == RET_SPECIAL) {
             nlr_raise(mp_obj_new_exception(&mp_type_KeyError));
@@ -280,8 +263,7 @@ STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     } else if (value == MP_OBJ_SENTINEL) {
         // load
         DBT key, val;
-        key.data = (void*)mp_obj_str_get_data(index, &v);
-        key.size = v;
+        key.data = (void*)mp_obj_str_get_data(index, &key.size);
         int res = __bt_get(self->db, &key, &val, 0);
         if (res == RET_SPECIAL) {
             nlr_raise(mp_obj_new_exception(&mp_type_KeyError));
@@ -291,10 +273,8 @@ STATIC mp_obj_t btree_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     } else {
         // store
         DBT key, val;
-        key.data = (void*)mp_obj_str_get_data(index, &v);
-        key.size = v;
-        val.data = (void*)mp_obj_str_get_data(value, &v);
-        val.size = v;
+        key.data = (void*)mp_obj_str_get_data(index, &key.size);
+        val.data = (void*)mp_obj_str_get_data(value, &val.size);
         int res = __bt_put(self->db, &key, &val, 0);
         CHECK_ERROR(res);
         return mp_const_none;
@@ -305,10 +285,8 @@ STATIC mp_obj_t btree_binary_op(mp_uint_t op, mp_obj_t lhs_in, mp_obj_t rhs_in)
     mp_obj_btree_t *self = MP_OBJ_TO_PTR(lhs_in);
     switch (op) {
         case MP_BINARY_OP_IN: {
-            mp_uint_t v;
             DBT key, val;
-            key.data = (void*)mp_obj_str_get_data(rhs_in, &v);
-            key.size = v;
+            key.data = (void*)mp_obj_str_get_data(rhs_in, &key.size);
             int res = __bt_get(self->db, &key, &val, 0);
             CHECK_ERROR(res);
             return mp_obj_new_bool(res != RET_SPECIAL);
diff --git a/extmod/modujson.c b/extmod/modujson.c
index ca4e6df104..bb2d452749 100644
--- a/extmod/modujson.c
+++ b/extmod/modujson.c
@@ -274,7 +274,7 @@ STATIC mp_obj_t mod_ujson_load(mp_obj_t stream_obj) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_ujson_load_obj, mod_ujson_load);
 
 STATIC mp_obj_t mod_ujson_loads(mp_obj_t obj) {
-    mp_uint_t len;
+    size_t len;
     const char *buf = mp_obj_str_get_data(obj, &len);
     vstr_t vstr = {len, len, (char*)buf, true};
     mp_obj_stringio_t sio = {{&mp_type_stringio}, &vstr, 0};
diff --git a/extmod/modure.c b/extmod/modure.c
index b8c242429b..7be091cc0d 100644
--- a/extmod/modure.c
+++ b/extmod/modure.c
@@ -96,7 +96,7 @@ STATIC mp_obj_t ure_exec(bool is_anchored, uint n_args, const mp_obj_t *args) {
     (void)n_args;
     mp_obj_re_t *self = MP_OBJ_TO_PTR(args[0]);
     Subject subj;
-    mp_uint_t len;
+    size_t len;
     subj.begin = mp_obj_str_get_data(args[1], &len);
     subj.end = subj.begin + len;
     int caps_num = (self->re.sub + 1) * 2;
@@ -128,7 +128,7 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(re_search_obj, 2, 4, re_search);
 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;
+    size_t len;
     subj.begin = mp_obj_str_get_data(args[1], &len);
     subj.end = subj.begin + len;
     int caps_num = (self->re.sub + 1) * 2;
diff --git a/extmod/modussl_mbedtls.c b/extmod/modussl_mbedtls.c
index a7b8a14405..40dd8c049f 100644
--- a/extmod/modussl_mbedtls.c
+++ b/extmod/modussl_mbedtls.c
@@ -156,13 +156,13 @@ STATIC mp_obj_ssl_socket_t *socket_new(mp_obj_t sock, struct ssl_args *args) {
     mbedtls_ssl_set_bio(&o->ssl, &o->sock, _mbedtls_ssl_send, _mbedtls_ssl_recv, NULL);
 
     if (args->key.u_obj != MP_OBJ_NULL) {
-        mp_uint_t key_len;
+        size_t key_len;
         const byte *key = (const byte*)mp_obj_str_get_data(args->key.u_obj, &key_len);
         // len should include terminating null
         ret = mbedtls_pk_parse_key(&o->pkey, key, key_len + 1, NULL, 0);
         assert(ret == 0);
 
-        mp_uint_t cert_len;
+        size_t cert_len;
         const byte *cert = (const byte*)mp_obj_str_get_data(args->cert.u_obj, &cert_len);
         // len should include terminating null
         ret = mbedtls_x509_crt_parse(&o->cert, cert, cert_len + 1);
diff --git a/extmod/modwebrepl.c b/extmod/modwebrepl.c
index 8e05809662..ce3c7dcbd5 100644
--- a/extmod/modwebrepl.c
+++ b/extmod/modwebrepl.c
@@ -308,7 +308,7 @@ STATIC mp_obj_t webrepl_close(mp_obj_t self_in) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(webrepl_close_obj, webrepl_close);
 
 STATIC mp_obj_t webrepl_set_password(mp_obj_t passwd_in) {
-    mp_uint_t len;
+    size_t len;
     const char *passwd = mp_obj_str_get_data(passwd_in, &len);
     if (len > sizeof(webrepl_passwd) - 1) {
         mp_raise_ValueError("");
diff --git a/extmod/vfs.c b/extmod/vfs.c
index 3ab8261dd2..e389ab324d 100644
--- a/extmod/vfs.c
+++ b/extmod/vfs.c
@@ -134,7 +134,7 @@ mp_obj_t mp_vfs_mount(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args
     mp_arg_parse_all(n_args - 2, pos_args + 2, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
     // get the mount point
-    mp_uint_t mnt_len;
+    size_t mnt_len;
     const char *mnt_str = mp_obj_str_get_data(pos_args[1], &mnt_len);
 
     // see if we need to auto-detect and create the filesystem
@@ -180,7 +180,7 @@ MP_DEFINE_CONST_FUN_OBJ_KW(mp_vfs_mount_obj, 2, mp_vfs_mount);
 mp_obj_t mp_vfs_umount(mp_obj_t mnt_in) {
     // remove vfs from the mount table
     mp_vfs_mount_t *vfs = NULL;
-    mp_uint_t mnt_len;
+    size_t mnt_len;
     const char *mnt_str = NULL;
     if (MP_OBJ_IS_STR(mnt_in)) {
         mnt_str = mp_obj_str_get_data(mnt_in, &mnt_len);