Index: l1-clos.lisp
===================================================================
--- l1-clos.lisp	(revision 12707)
+++ l1-clos.lisp	(working copy)
@@ -255,7 +255,7 @@
         (extract-instance-and-class-slotds (call-next-method))
       (setq instance-slots (sort-effective-instance-slotds instance-slots class cpl))
       (do* ((loc 1 (1+ loc))
-            (islotds instance-slots (cdr islotds)))
+            (islotds (remove-if-not (lambda (x) (eq :instance (%slot-definition-allocation x)))  instance-slots) (cdr islotds)))
            ((null islotds))
         (declare (fixnum loc))
         (setf (%slot-definition-location (car islotds)) loc))