diff --git a/src/library/type_context.h b/src/library/type_context.h
index 05a8e02abb..25f07c47d5 100644
--- a/src/library/type_context.h
+++ b/src/library/type_context.h
@@ -714,7 +714,7 @@ public:
     virtual environment const & env() const override { return m_cache->m_env; }
 
     // TODO(Leo): avoid ::lean::mk_fresh_name
-    virtual name mk_fresh_name() { return ::lean::mk_fresh_name(); }
+    virtual name mk_fresh_name() override { return ::lean::mk_fresh_name(); }
 
     options const & get_options() const { return m_cache->m_options; }
     local_context const & lctx() const { return m_lctx; }