diff --git a/jerry-core/ecma/operations/ecma-objects.c b/jerry-core/ecma/operations/ecma-objects.c
index 2dc872fa3..f4d1ae1db 100644
--- a/jerry-core/ecma/operations/ecma-objects.c
+++ b/jerry-core/ecma/operations/ecma-objects.c
@@ -2415,10 +2415,12 @@ ecma_op_object_own_property_keys (ecma_object_t *obj_p) /**< object */
       {
         ecma_property_pair_t *prop_pair_p = (ecma_property_pair_t *) prop_iter_p;
 
-        /* Internal properties are special properties so they must not be present. */
-        JERRY_ASSERT (ECMA_PROPERTY_GET_NAME_TYPE (*property_p) != ECMA_DIRECT_STRING_MAGIC
-                      || prop_pair_p->names_cp[i] < LIT_NON_INTERNAL_MAGIC_STRING__COUNT
-                      || prop_pair_p->names_cp[i] >= LIT_MAGIC_STRING__COUNT);
+        if (ECMA_PROPERTY_GET_NAME_TYPE (*property_p) == ECMA_DIRECT_STRING_MAGIC
+            && prop_pair_p->names_cp[i] >= LIT_NON_INTERNAL_MAGIC_STRING__COUNT
+            && prop_pair_p->names_cp[i] < LIT_MAGIC_STRING__COUNT)
+        {
+          continue;
+        }
 
         ecma_string_t *name_p = ecma_string_from_property_name (*property_p,
                                                                 prop_pair_p->names_cp[i]);