diff --git a/src/proto/mbyte.pro b/src/proto/mbyte.pro
index 8af1cc2..9bff4d3 100644
--- a/src/proto/mbyte.pro
+++ b/src/proto/mbyte.pro
@@ -55,6 +55,7 @@
 void mb_adjustpos __ARGS((pos_T *lp));
 char_u *mb_prevptr __ARGS((char_u *line, char_u *p));
 int mb_charlen __ARGS((char_u *str));
+int mb_charlen_len __ARGS((char_u *str, int len));
 char_u *mb_unescape __ARGS((char_u **pp));
 int mb_lefthalve __ARGS((int row, int col));
 int mb_fix_col __ARGS((int col, int row));