diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 8f0c0c3..2660d93 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -105,8 +105,17 @@
   endif
 
   " Close any extra windows and make the current one not modified.
-  while winnr('$') > 1
+  while 1
+    let wincount = winnr('$')
+    if wincount == 1
+      break
+    endif
     bwipe!
+    if wincount == winnr('$')
+      " Did not manage to close a window.
+      only!
+      break
+    endif
   endwhile
   set nomodified
 endfunc