diff --git a/expac.c b/expac.c
index a0b8edc..e08b9f2 100644
--- a/expac.c
+++ b/expac.c
@@ -88,7 +88,7 @@ static char *strtrim(char *str) {
   return str;
 }
 
-char *trim_optdep(char *optdep) {
+static char *trim_optdep(char *optdep) {
   char *colon;
 
   colon = strchr(optdep, ':');