diff --git a/ext/ripper/ripper_init.c.tmpl b/ext/ripper/ripper_init.c.tmpl
index 40c583eeae..0008eb9fd0 100644
--- a/ext/ripper/ripper_init.c.tmpl
+++ b/ext/ripper/ripper_init.c.tmpl
@@ -1,3 +1,4 @@
+%# -*- c -*-
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
 #include "internal.h"