diff --git a/dune/gfe/cosseratenergystiffness.hh b/dune/gfe/cosseratenergystiffness.hh
index 140d82ad1f02cbac4e7bb782b4bdaa7c1bdd7e76..7868e45e4785637290f7c849740cf4c0cb713a29 100644
--- a/dune/gfe/cosseratenergystiffness.hh
+++ b/dune/gfe/cosseratenergystiffness.hh
@@ -551,7 +551,8 @@ energy(const Entity& element,
     //   Assemble boundary contributions
     //////////////////////////////////////////////////////////////////////////////
 
-    assert(neumannFunction_);
+    if (not neumannFunction_)
+        return energy;
 
     for (typename Entity::LeafIntersectionIterator it = element.ileafbegin(); it != element.ileafend(); ++it) {
 
@@ -992,8 +993,6 @@ assembleGradient(const Entity& element,
     //   Assemble boundary contributions
     //////////////////////////////////////////////////////////////////////////////
 
-    assert(neumannFunction_);
-
     for (typename Entity::LeafIntersectionIterator it = element.ileafbegin(); it != element.ileafend(); ++it) {
 
         if (not neumannBoundary_ or not neumannBoundary_->contains(*it))