diff --git a/src/core/ns-unknown.cc b/src/core/ns-unknown.cc
index a7fef9a28..92be9cbfd 100644
--- a/src/core/ns-unknown.cc
+++ b/src/core/ns-unknown.cc
@@ -372,6 +372,9 @@ InterfaceTest::RunTests (void)
       ok = false;
     }
 
+  // the following cannot work and it is on purpose
+  // delete derived;
+
   return ok;
 }