diff --git a/src/options.h b/src/options.h
index b03e9f0..bf8fbd0 100644
--- a/src/options.h
+++ b/src/options.h
@@ -56,4 +56,5 @@ struct option_t
 
 extern struct option_t option;
 
+long string_to_long(char *string);
 void parse_options(int argc, char *argv[]);