diff --git a/regint.h b/regint.h
index f7e44720e0..164828f430 100644
--- a/regint.h
+++ b/regint.h
@@ -816,7 +816,7 @@ typedef st_data_t hash_data_type;
 typedef unsigned long hash_data_type;
 #endif
 
-extern hash_table_type* onig_st_init_strend_table_with_size P_((int size));
+extern hash_table_type* onig_st_init_strend_table_with_size P_((st_index_t size));
 extern int onig_st_lookup_strend P_((hash_table_type* table, const UChar* str_key, const UChar* end_key, hash_data_type *value));
 extern int onig_st_insert_strend P_((hash_table_type* table, const UChar* str_key, const UChar* end_key, hash_data_type value));