diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index b9d85f4..b1e0528 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -188,8 +188,9 @@
   au!
   au SwapExists * call HandleSwapExists()
 
-  " Close any stray popup windows.
+  " Check for and close any stray popup windows.
   if has('popupwin')
+    call assert_equal([], popup_list())
     call popup_clear(1)
   endif