diff --git a/sys/src/9/xen/mmu.c b/sys/src/9/xen/mmu.c
index b3ce84074..cd51b47ff 100644
--- a/sys/src/9/xen/mmu.c
+++ b/sys/src/9/xen/mmu.c
@@ -349,7 +349,7 @@ mmurelease(Proc* proc)
 	for(page = proc->mmufree; page; page = next){
 		next = page->next;
 		if(--page->ref)
-			panic("mmurelease: page->ref %d\n", page->ref);
+			panic("mmurelease: page->ref %ld\n", page->ref);
 		pagechainhead(page);
 	}
 	if(proc->mmufree && palloc.r.p)