diff --git a/src/util/max_cliques.h b/src/util/max_cliques.h
index bb7b0b490..ec888c84b 100644
--- a/src/util/max_cliques.h
+++ b/src/util/max_cliques.h
@@ -24,6 +24,8 @@ Notes:
 
 template<class T>
 class max_cliques : public T {
+    using T::negate;
+
     vector<unsigned_vector> m_next, m_tc;
     uint_set                m_reachable[2];
     uint_set                m_seen1, m_seen2;