diff --git a/gtk/gtkbuiltinicon.c b/gtk/gtkbuiltinicon.c
index 8a57a617fa..a6974e6e13 100644
--- a/gtk/gtkbuiltinicon.c
+++ b/gtk/gtkbuiltinicon.c
@@ -271,7 +271,7 @@ gtk_builtin_icon_get_default_size_property (GtkBuiltinIcon *icon)
 {
   GtkBuiltinIconPrivate *priv;
 
-  g_return_val_if_fail (GTK_IS_BUILTIN_ICON (icon), GTK_CSS_IMAGE_BUILTIN_NONE);
+  g_return_val_if_fail (GTK_IS_BUILTIN_ICON (icon), NULL);
 
   priv = gtk_builtin_icon_get_instance_private (icon);