diff --git a/cbits/mk_wcwidth.c b/cbits/mk_wcwidth.c
index feaa163..59dec6b 100644
--- a/cbits/mk_wcwidth.c
+++ b/cbits/mk_wcwidth.c
@@ -141,7 +141,7 @@ static int vty_bisearch(HsChar ucs, const struct interval *table, int max) {
  * in ISO 10646.
  */
 
-HsInt builtin_wcwidth(HsChar ucs)
+static HsInt builtin_wcwidth(HsChar ucs)
 {
   /* sorted list of non-overlapping intervals of non-spacing characters */
   /* generated by "uniset +cat=Me +cat=Mn +cat=Cf -00AD +1160-11FF +200B c" */