diff --git a/sys/vm/vm_kern.c b/sys/vm/vm_kern.c
--- a/sys/vm/vm_kern.c
+++ b/sys/vm/vm_kern.c
@@ -217,6 +217,8 @@
 	int cow;
 
 	size = round_page(size);
+	if (size == 0)
+		return (0);
 
 	if (kmflags & KM_KRESERVE)
 		count = vm_map_entry_kreserve(MAP_RESERVE_COUNT);