diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index a4c238e..db6797d 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -246,8 +246,7 @@
   endif
 
   if filereadable('guidialogfile')
-    call add(v:errors, "Unexpected dialog:")
-    call add(v:errors, readfile('guidialogfile').join('\n'))
+    call add(v:errors, "Unexpected dialog: " .. readfile('guidialogfile')->join('<NL>'))
     call delete('guidialogfile')
   endif