diff --git a/gtk/gtkbuilderparser.c b/gtk/gtkbuilderparser.c
index ccfb1cbc56..c2afb64579 100644
--- a/gtk/gtkbuilderparser.c
+++ b/gtk/gtkbuilderparser.c
@@ -1409,13 +1409,13 @@ expression_info_construct (GtkBuilder      *builder,
             return NULL;
           }
 
-        if (g_type_is_a (type, G_TYPE_OBJECT))
+        if (g_type_fundamental (type) == G_TYPE_OBJECT)
           {
             GObjectClass *class = g_type_class_ref (type);
             pspec = g_object_class_find_property (class, info->property.property_name);
             g_type_class_unref (class);
           }
-        else if (g_type_is_a (type, G_TYPE_INTERFACE))
+        else if (g_type_fundamental (type) == G_TYPE_INTERFACE)
           {
             GTypeInterface *iface = g_type_default_interface_ref (type);
             pspec = g_object_interface_find_property (iface, info->property.property_name);