diff --git a/mrbgems/mruby-string-utf8/src/string.c b/mrbgems/mruby-string-utf8/src/string.c
index da348f4fb..7ce3b9f75 100644
--- a/mrbgems/mruby-string-utf8/src/string.c
+++ b/mrbgems/mruby-string-utf8/src/string.c
@@ -1,12 +1,10 @@
 #include "mruby.h"
 #include "mruby/string.h"
 #include "mruby/range.h"
+#include "mruby/re.h"
 #include <ctype.h>
 #include <string.h>
 
-/* TODO: duplicate definition in src/re.h */
-#define REGEXP_CLASS "Regexp"
-
 static const char utf8len_codepage[256] =
 {
   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,