diff --git a/src/libecmabuiltins/ecma-builtin-internal-routines-template.inc.h b/src/libecmabuiltins/ecma-builtin-internal-routines-template.inc.h
index f3efa31df..06f30f96c 100644
--- a/src/libecmabuiltins/ecma-builtin-internal-routines-template.inc.h
+++ b/src/libecmabuiltins/ecma-builtin-internal-routines-template.inc.h
@@ -109,8 +109,10 @@ TRY_TO_INSTANTIATE_PROPERTY_ROUTINE_NAME (BUILTIN_UNDERSCORED_ID) (ecma_object_t
 
   ecma_magic_string_id_t id;
 
-  bool is_string_magic = ecma_is_string_magic (prop_name_p, &id);
-  JERRY_ASSERT (is_string_magic);
+  if (!ecma_is_string_magic (prop_name_p, &id))
+  {
+    return NULL;
+  }
 
   int32_t index;
   index = ecma_builtin_bin_search_for_magic_string_id_in_array (ecma_builtin_property_names,
diff --git a/src/libecmaoperations/ecma-objects.c b/src/libecmaoperations/ecma-objects.c
index eccc5bf11..f23b9ba2b 100644
--- a/src/libecmaoperations/ecma-objects.c
+++ b/src/libecmaoperations/ecma-objects.c
@@ -104,11 +104,8 @@ ecma_op_object_get_own_property (ecma_object_t *obj_p, /**< the object */
 
   if (unlikely (prop_p == NULL))
   {
-    ecma_magic_string_id_t magic_string_id __unused;
-
     if (is_builtin
-        && type != ECMA_OBJECT_TYPE_BUILT_IN_FUNCTION
-        && ecma_is_string_magic (property_name_p, &magic_string_id))
+        && type != ECMA_OBJECT_TYPE_BUILT_IN_FUNCTION)
     {
       prop_p = ecma_builtin_try_to_instantiate_property (obj_p, property_name_p);
     }