--- a/include/util.h
+++ b/include/util.h
@@ -449,6 +449,11 @@ struct slice_allocator
   {
     p->~Tp ();
   }
+
+  bool operator ==(const slice_allocator &) const
+  {
+    return true;
+  }
 };
 
 // basically a memory area, but refcounted