diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index d5765d1..133993d 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -215,7 +215,7 @@
 for name in s:GetSwapFileList()
   call delete(name)
 endfor
-unlet name
+unlet! name
 
 
 " Invoked when a test takes too much time.