diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 3ff8c67..08b1f8e 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -227,7 +227,12 @@
 
   " Close any extra tab pages and windows and make the current one not modified.
   while tabpagenr('$') > 1
+    let winid = win_getid()
     quit!
+    if winid == win_getid()
+      echoerr 'Could not quit window'
+      break
+    endif
   endwhile
 
   while 1