diff --git a/src/proto/mbyte.pro b/src/proto/mbyte.pro
index bb00a50..0e41a41 100644
--- a/src/proto/mbyte.pro
+++ b/src/proto/mbyte.pro
@@ -10,6 +10,7 @@
 int latin_char2bytes(int c, char_u *buf);
 int latin_ptr2len(char_u *p);
 int latin_ptr2len_len(char_u *p, int size);
+int utf_ambiguous_width(int c);
 int utf_char2cells(int c);
 int latin_ptr2cells(char_u *p);
 int utf_ptr2cells(char_u *p);