diff --git a/src/or/connection.c b/src/or/connection.c
index b8aa3df98..97d218793 100644
--- a/src/or/connection.c
+++ b/src/or/connection.c
@@ -404,7 +404,7 @@ connection_about_to_close_connection(connection_t *conn)
   edge_connection_t *edge_conn;
   time_t now = time(NULL);
 
-  assert(conn->marked_for_close);
+  tor_assert(conn->marked_for_close);
 
   if (CONN_IS_EDGE(conn)) {
     if (!conn->edge_has_sent_end) {