--- clg-0.93-pristine/glib/gobject.lisp	2007-06-01 06:46:15.000000000 -0400
+++ clg-0.93-patched/glib/gobject.lisp	2008-12-15 10:22:08.798932680 -0500
@@ -551,6 +551,10 @@
   (let ((supers (cons (supertype type) (implements type)))
 	(class  (type-from-number type))
 	(slots (getf options :slots)))
+    (unless (car supers)
+      (error "Introspected type ~D (~A) has unknown supertype ~D (~A)"
+	     type (find-foreign-type-name type)
+	     (type-parent type) (find-foreign-type-name (type-parent type))))
     `(defclass ,class ,supers
 	 ,(unless forward-p
 	    (slot-definitions class (query-object-class-properties type) slots))