diff --git a/src/testdir/shared.vim b/src/testdir/shared.vim
index 1032b45..cf15a4c 100644
--- a/src/testdir/shared.vim
+++ b/src/testdir/shared.vim
@@ -278,6 +278,9 @@
   let cmd = substitute(cmd, '-u NONE', '--clean', '')
   let cmd = substitute(cmd, '--not-a-term', '', '')
 
+  " Force using utf-8, Vim may pick up something else from the environment.
+  let cmd ..= ' --cmd "set enc=utf8" '
+
   " Optionally run Vim under valgrind
   " let cmd = 'valgrind --tool=memcheck --leak-check=yes --num-callers=25 --log-file=valgrind ' . cmd