diff --git a/src/racket/gc2/immobile_boxes.c b/src/racket/gc2/immobile_boxes.c
index b67d27492f..cc903c4fed 100644
--- a/src/racket/gc2/immobile_boxes.c
+++ b/src/racket/gc2/immobile_boxes.c
@@ -17,8 +17,10 @@ void **GC_malloc_immobile_box(void *p)
 void GC_free_immobile_box(void **b) 
 {
   GCTYPE *gc = GC_get_GC();
-  GC_Immobile_Box *ib;
+  GC_Immobile_Box *ib = (GC_Immobile_Box *)b;
 
+#if 0
+  /* For debugging: */
   for(ib = gc->immobile_boxes; ib; ib = ib->next)
     if(PPTR(ib) == b) {
       if(ib->prev) ib->prev->next = ib->next;
@@ -28,6 +30,12 @@ void GC_free_immobile_box(void **b)
       return;
     }
   GCWARN((GCOUTF, "Attempted free of non-existent immobile box %p\n", b));
+#else
+  if(ib->prev) ib->prev->next = ib->next;
+  if(!ib->prev) gc->immobile_boxes = ib->next;
+  if(ib->next) ib->next->prev = ib->prev;
+  free(ib);
+#endif
 }
 
 #define traverse_immobiles(gcMUCK, set_bt_src) {			  \