diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index d4c42f3..766f983 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -410,6 +410,9 @@
   endtry
 endif
 
+" Delete the .res file, it may change behavior for completion
+call delete(fnamemodify(g:testname, ':r') .. '.res')
+
 " Locate Test_ functions and execute them.
 redir @q
 silent function /^Test_