diff --git a/servers/vm/mmap.c b/servers/vm/mmap.c
index 5abc459b6..686db4779 100644
--- a/servers/vm/mmap.c
+++ b/servers/vm/mmap.c
@@ -374,7 +374,8 @@ PUBLIC int do_munmap(message *m)
         }
  
 	len = m->VMUM_LEN;
-	len -= len % VM_PAGE_SIZE;
+	if (len % VM_PAGE_SIZE)
+		len += VM_PAGE_SIZE - (len % VM_PAGE_SIZE);
 
         if(addr != vr->vaddr || len > vr->length || len < VM_PAGE_SIZE) {
                 return EFAULT;