diff --git a/hash.c b/hash.c
index 61b9c9a3cd..f4fc3dc04f 100644
--- a/hash.c
+++ b/hash.c
@@ -2854,7 +2854,7 @@ keep_if_i(VALUE key, VALUE value, VALUE hash)
  *  Hash#filter! is an alias for Hash#select!.
  */
 
-VALUE
+static VALUE
 rb_hash_select_bang(VALUE hash)
 {
     st_index_t n;