diff --git a/include/mes/builtins.h b/include/mes/builtins.h
index 14f0f8a6..fed49aef 100644
--- a/include/mes/builtins.h
+++ b/include/mes/builtins.h
@@ -73,6 +73,7 @@ struct scm *hash_table_printer (struct scm *table);
 struct scm *make_hash_table (struct scm *x);
 struct scm *hash_table_p (struct scm *x);
 struct scm *hash_map_to_list (struct scm *proc, struct scm *table);
+struct scm *hash_clear_x (struct scm *table);
 /* src/lib.c */
 struct scm *type_ (struct scm *x);
 struct scm *car_ (struct scm *x);
diff --git a/src/builtins.c b/src/builtins.c
index 5b5dee69..e50214aa 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -183,6 +183,7 @@ mes_builtins (struct scm *a)            /*:((internal)) */
   a = init_builtin (builtin_type, "hash-table?", 1, &hash_table_p, a);
   a = init_builtin (builtin_type, "make-hash-table", -1, &make_hash_table, a);
   a = init_builtin (builtin_type, "hash-map->list", 2, &hash_map_to_list, a);
+  a = init_builtin (builtin_type, "hash-clear!", 1, &hash_clear_x, a);
   /* src/lib.c */
   a = init_builtin (builtin_type, "core:type", 1, &type_, a);
   a = init_builtin (builtin_type, "core:car", 1, &car_, a);
diff --git a/src/hash.c b/src/hash.c
index f898b41e..7e9187de 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -248,3 +248,13 @@ hash_map_to_list (struct scm *proc, struct scm *table)
     }
   return lst;
 }
+
+struct scm *
+hash_clear_x (struct scm *table)
+{
+  struct scm *s = struct_ref_ (table, 3);
+  long size = s->value;
+  struct scm *buckets = make_vector_ (size, cell_unspecified);
+  struct_set_x_ (table, 4, buckets);
+  return cell_unspecified;
+}