diff --git a/src/testdir/test_cdo.in b/src/testdir/test_cdo.in
index fb80ea1..087cd2e 100644
--- a/src/testdir/test_cdo.in
+++ b/src/testdir/test_cdo.in
@@ -2,6 +2,7 @@
 
 STARTTEST
 :so small.vim
+:lang mess C
 :if !has('quickfix') | e! test.ok | wq! test.out | endif
 
 :call writefile(["Line1", "Line2", "Line3"], 'Xtestfile1')