Index: sys/vm/memguard.c
===================================================================
--- sys/vm/memguard.c	(revision 285128)
+++ sys/vm/memguard.c	(working copy)
@@ -351,7 +351,10 @@
 		addr = (vm_offset_t)NULL;
 		goto out;
 	}
-	memguard_cursor = addr + size_v;
+	if (do_guard)
+		memguard_cursor = addr + size_v - PAGE_SIZE;
+	else
+		memguard_cursor = addr + size_v;
 	*v2sizep(trunc_page(addr)) = req_size;
 	*v2sizev(trunc_page(addr)) = size_v;
 	memguard_succ++;