diff --git a/src/proto/syntax.pro b/src/proto/syntax.pro
index be34258..33b8b80 100644
--- a/src/proto/syntax.pro
+++ b/src/proto/syntax.pro
@@ -23,6 +23,7 @@
 char_u *get_syntime_arg(expand_T *xp, int idx);
 void init_highlight(int both, int reset);
 int load_colors(char_u *name);
+int lookup_color(int idx, int foreground);
 void do_highlight(char_u *line, int forceit, int init);
 void free_highlight(void);
 void restore_cterm_colors(void);