diff --git a/py/bc.c b/py/bc.c
index e002bca26..e1795ce41 100644
--- a/py/bc.c
+++ b/py/bc.c
@@ -213,6 +213,7 @@ STATIC void mp_setup_code_state_helper(mp_code_state_t *code_state, size_t n_arg
                 #endif
                 if (wanted_arg_name == MP_OBJ_NEW_QSTR(arg_qstr)) {
                     if (code_state_state[n_state - 1 - j] != MP_OBJ_NULL) {
+                    error_multiple:
                         mp_raise_msg_varg(&mp_type_TypeError,
                             MP_ERROR_TEXT("function got multiple values for argument '%q'"), MP_OBJ_QSTR_VALUE(wanted_arg_name));
                     }
@@ -229,7 +230,12 @@ STATIC void mp_setup_code_state_helper(mp_code_state_t *code_state, size_t n_arg
                     MP_ERROR_TEXT("unexpected keyword argument '%q'"), MP_OBJ_QSTR_VALUE(wanted_arg_name));
                 #endif
             }
-            mp_obj_dict_store(dict, kwargs[2 * i], kwargs[2 * i + 1]);
+            mp_map_elem_t *elem = mp_map_lookup(mp_obj_dict_get_map(dict), wanted_arg_name, MP_MAP_LOOKUP_ADD_IF_NOT_FOUND);
+            if (elem->value == MP_OBJ_NULL) {
+                elem->value = kwargs[2 * i + 1];
+            } else {
+                goto error_multiple;
+            }
         continue2:;
         }
 
diff --git a/tests/basics/fun_calldblstar.py b/tests/basics/fun_calldblstar.py
index 4a503698f..0308f42bd 100644
--- a/tests/basics/fun_calldblstar.py
+++ b/tests/basics/fun_calldblstar.py
@@ -20,3 +20,13 @@ class A:
 a = A()
 a.f(1, **{'b':2})
 a.f(1, **{'b':val for val in range(1)})
+
+# test for duplicate keys in **kwargs not allowed
+
+def f1(**kwargs):
+    print(kwargs)
+
+try:
+    f1(**{'a': 1, 'b': 2}, **{'b': 3, 'c': 4})
+except TypeError:
+    print('TypeError')