diff --git a/src/proto/option.pro b/src/proto/option.pro
index 9c58c3e..d14c89b 100644
--- a/src/proto/option.pro
+++ b/src/proto/option.pro
@@ -19,6 +19,7 @@
 void set_term_option_alloced __ARGS((char_u **p));
 int was_set_insecurely __ARGS((char_u *opt, int opt_flags));
 void set_string_option_direct __ARGS((char_u *name, int opt_idx, char_u *val, int opt_flags, int set_sid));
+char_u *check_colorcolumn __ARGS((win_T *wp));
 char_u *check_stl_option __ARGS((char_u *s));
 int get_option_value __ARGS((char_u *name, long *numval, char_u **stringval, int opt_flags));
 void set_option_value __ARGS((char_u *name, long number, char_u *string, int opt_flags));