diff --git a/src/proto/spell.pro b/src/proto/spell.pro
index 16eb19d..9fc7a74 100644
--- a/src/proto/spell.pro
+++ b/src/proto/spell.pro
@@ -9,7 +9,7 @@
 void put_bytes __ARGS((FILE *fd, long_u nr, int len));
 void ex_mkspell __ARGS((exarg_T *eap));
 void ex_spell __ARGS((exarg_T *eap));
-void spell_add_word __ARGS((char_u *word, int len, int bad, int index));
+void spell_add_word __ARGS((char_u *word, int len, int bad, int index, int undo));
 void init_spell_chartab __ARGS((void));
 int spell_check_sps __ARGS((void));
 void spell_suggest __ARGS((int count));