diff --git a/py/objstr.c b/py/objstr.c
index 130af8a6af..dd44b0784d 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -93,17 +93,16 @@ void mp_str_print_quoted(void (*print)(void *env, const char *fmt, ...), void *e
 }
 
 #if MICROPY_PY_UJSON
-STATIC void str_print_json(void (*print)(void *env, const char *fmt, ...), void *env, const byte *str_data, mp_uint_t str_len) {
+void mp_str_print_json(void (*print)(void *env, const char *fmt, ...), void *env, const byte *str_data, mp_uint_t str_len) {
+    // for JSON spec, see http://www.ietf.org/rfc/rfc4627.txt
+    // if we are given a valid utf8-encoded string, we will print it in a JSON-conforming way
     print(env, "\"");
     for (const byte *s = str_data, *top = str_data + str_len; s < top; s++) {
-        if (*s == '"' || *s == '\\' || *s == '/') {
+        if (*s == '"' || *s == '\\') {
             print(env, "\\%c", *s);
-        } else if (32 <= *s && *s <= 126) {
+        } else if (*s >= 32) {
+            // this will handle normal and utf-8 encoded chars
             print(env, "%c", *s);
-        } else if (*s == '\b') {
-            print(env, "\\b");
-        } else if (*s == '\f') {
-            print(env, "\\f");
         } else if (*s == '\n') {
             print(env, "\\n");
         } else if (*s == '\r') {
@@ -111,6 +110,7 @@ STATIC void str_print_json(void (*print)(void *env, const char *fmt, ...), void
         } else if (*s == '\t') {
             print(env, "\\t");
         } else {
+            // this will handle control chars
             print(env, "\\u%04x", *s);
         }
     }
@@ -120,13 +120,13 @@ STATIC void str_print_json(void (*print)(void *env, const char *fmt, ...), void
 
 STATIC void str_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t self_in, mp_print_kind_t kind) {
     GET_STR_DATA_LEN(self_in, str_data, str_len);
-    bool is_bytes = MP_OBJ_IS_TYPE(self_in, &mp_type_bytes);
     #if MICROPY_PY_UJSON
     if (kind == PRINT_JSON) {
-        str_print_json(print, env, str_data, str_len);
+        mp_str_print_json(print, env, str_data, str_len);
         return;
     }
     #endif
+    bool is_bytes = MP_OBJ_IS_TYPE(self_in, &mp_type_bytes);
     if (kind == PRINT_STR && !is_bytes) {
         print(env, "%.*s", str_len, str_data);
     } else {
diff --git a/py/objstr.h b/py/objstr.h
index 3d20680d34..8cd4852943 100644
--- a/py/objstr.h
+++ b/py/objstr.h
@@ -50,6 +50,7 @@ typedef struct _mp_obj_str_t {
     { str_data = qstr_data(MP_OBJ_QSTR_VALUE(str_obj_in), &str_len); } \
     else { str_len = ((mp_obj_str_t*)str_obj_in)->len; str_data = ((mp_obj_str_t*)str_obj_in)->data; }
 
+void mp_str_print_json(void (*print)(void *env, const char *fmt, ...), void *env, const byte *str_data, mp_uint_t str_len);
 mp_obj_t mp_obj_str_format(mp_uint_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, mp_uint_t len);
 
diff --git a/py/objstrunicode.c b/py/objstrunicode.c
index 0ee7f1dc9a..062e011fb1 100644
--- a/py/objstrunicode.c
+++ b/py/objstrunicode.c
@@ -91,41 +91,11 @@ STATIC void uni_print_quoted(void (*print)(void *env, const char *fmt, ...), voi
     print(env, "%c", quote_char);
 }
 
-#if MICROPY_PY_UJSON
-STATIC void uni_print_json(void (*print)(void *env, const char *fmt, ...), void *env, const byte *str_data, uint str_len) {
-    print(env, "\"");
-    const byte *s = str_data, *top = str_data + str_len;
-    while (s < top) {
-        unichar ch;
-        ch = utf8_get_char(s);
-        s = utf8_next_char(s);
-        if (ch == '"' || ch == '\\' || ch == '/') {
-            print(env, "\\%c", ch);
-        } else if (32 <= ch && ch <= 126) {
-            print(env, "%c", ch);
-        } else if (*s == '\b') {
-            print(env, "\\b");
-        } else if (*s == '\f') {
-            print(env, "\\f");
-        } else if (*s == '\n') {
-            print(env, "\\n");
-        } else if (*s == '\r') {
-            print(env, "\\r");
-        } else if (*s == '\t') {
-            print(env, "\\t");
-        } else {
-            print(env, "\\u%04x", ch);
-        }
-    }
-    print(env, "\"");
-}
-#endif
-
 STATIC void uni_print(void (*print)(void *env, const char *fmt, ...), void *env, mp_obj_t self_in, mp_print_kind_t kind) {
     GET_STR_DATA_LEN(self_in, str_data, str_len);
     #if MICROPY_PY_UJSON
     if (kind == PRINT_JSON) {
-        uni_print_json(print, env, str_data, str_len);
+        mp_str_print_json(print, env, str_data, str_len);
         return;
     }
     #endif
diff --git a/tests/extmod/ujson_dumps.py b/tests/extmod/ujson_dumps.py
index 6e858fd3f9..0b8d239a06 100644
--- a/tests/extmod/ujson_dumps.py
+++ b/tests/extmod/ujson_dumps.py
@@ -9,7 +9,7 @@ print(json.dumps(None))
 print(json.dumps(1))
 print(json.dumps(1.2))
 print(json.dumps('abc'))
-print(json.dumps('\x01\x7e\x7f\x80\u1234'))
+print(json.dumps('\x00\x01\x7e'))
 print(json.dumps([]))
 print(json.dumps([1]))
 print(json.dumps([1, 2]))