diff --git a/py/obj.h b/py/obj.h
index 2779b3f86..80599966e 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -720,6 +720,7 @@ qstr mp_obj_str_get_qstr(mp_obj_t self_in); // use this if you will anyway conve
 const char *mp_obj_str_get_str(mp_obj_t self_in); // use this only if you need the string to be null terminated
 const char *mp_obj_str_get_data(mp_obj_t self_in, size_t *len);
 mp_obj_t mp_obj_str_intern(mp_obj_t str);
+mp_obj_t mp_obj_str_intern_checked(mp_obj_t obj);
 void mp_str_print_quoted(const mp_print_t *print, const byte *str_data, size_t str_len, bool is_bytes);
 
 #if MICROPY_PY_BUILTINS_FLOAT
diff --git a/py/objstr.c b/py/objstr.c
index c42f38e75..0b11533f8 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -2062,6 +2062,12 @@ mp_obj_t mp_obj_str_intern(mp_obj_t str) {
     return mp_obj_new_str_via_qstr((const char*)data, len);
 }
 
+mp_obj_t mp_obj_str_intern_checked(mp_obj_t obj) {
+    size_t len;
+    const char *data = mp_obj_str_get_data(obj, &len);
+    return mp_obj_new_str_via_qstr((const char*)data, len);
+}
+
 mp_obj_t mp_obj_new_bytes(const byte* data, size_t len) {
     return mp_obj_new_str_copy(&mp_type_bytes, data, len);
 }
diff --git a/py/runtime.c b/py/runtime.c
index 54ec0d70b..ca68fe982 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -748,8 +748,8 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
             if (MP_MAP_SLOT_IS_FILLED(map, i)) {
                 // the key must be a qstr, so intern it if it's a string
                 mp_obj_t key = map->table[i].key;
-                if (MP_OBJ_IS_TYPE(key, &mp_type_str)) {
-                    key = mp_obj_str_intern(key);
+                if (!MP_OBJ_IS_QSTR(key)) {
+                    key = mp_obj_str_intern_checked(key);
                 }
                 args2[args2_len++] = key;
                 args2[args2_len++] = map->table[i].value;
@@ -778,8 +778,8 @@ void mp_call_prepare_args_n_kw_var(bool have_self, size_t n_args_n_kw, const mp_
             }
 
             // the key must be a qstr, so intern it if it's a string
-            if (MP_OBJ_IS_TYPE(key, &mp_type_str)) {
-                key = mp_obj_str_intern(key);
+            if (!MP_OBJ_IS_QSTR(key)) {
+                key = mp_obj_str_intern_checked(key);
             }
 
             // get the value corresponding to the key
diff --git a/tests/basics/fun_calldblstar.py b/tests/basics/fun_calldblstar.py
index aae9828cf..4a503698f 100644
--- a/tests/basics/fun_calldblstar.py
+++ b/tests/basics/fun_calldblstar.py
@@ -6,6 +6,11 @@ def f(a, b):
 f(1, **{'b':2})
 f(1, **{'b':val for val in range(1)})
 
+try:
+    f(1, **{len:2})
+except TypeError:
+    print('TypeError')
+
 # test calling a method with keywords given by **dict
 
 class A: