diff --git a/src/lisp/gencgc.c b/src/lisp/gencgc.c
index f06b23b6f7d6ae269997fab15b16974f251e83d1..a9c3e96bb03f17d58599075705de0db3a58a31ec 100644
--- a/src/lisp/gencgc.c
+++ b/src/lisp/gencgc.c
@@ -1194,7 +1194,7 @@ gc_alloc_new_region(int nbytes, int unboxed, struct alloc_region *alloc_region)
 	for (p = (int *) alloc_region->start_addr;
 	     p < (int *) alloc_region->end_addr; p++)
 	    if (*p != 0)
-		fprintf(stderr, "** new region not zero @ %lx: %lx\n",
+		fprintf(stderr, "** new region not zero @ %lx: %x\n",
 			(unsigned long) p, *p);
     }