diff --git a/src/testdir/test39.in b/src/testdir/test39.in
index a16d4d9..d39ba82 100644
--- a/src/testdir/test39.in
+++ b/src/testdir/test39.in
@@ -5,6 +5,8 @@
 STARTTEST
 :so small.vim
 :so mbyte.vim
+:" This only works when 'encoding' is "latin1", don't depend on the environment
+:set enc=latin1
 /^abcde
 :" Test shift-right of a block
 jlllljj>wlljlll>