diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 766f983..a4c238e 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -245,6 +245,12 @@
     call popup_clear(1)
   endif
 
+  if filereadable('guidialogfile')
+    call add(v:errors, "Unexpected dialog:")
+    call add(v:errors, readfile('guidialogfile').join('\n'))
+    call delete('guidialogfile')
+  endif
+
   " Close any extra tab pages and windows and make the current one not modified.
   while tabpagenr('$') > 1
     let winid = win_getid()