diff --git a/dumux/boxmodels/2p2cni/2p2cnivolumevariables.hh b/dumux/boxmodels/2p2cni/2p2cnivolumevariables.hh
index 2913f51005c21600c053fef6d6197a211e60bef2..c6712a89e036d04c7bc037a43ab0e192bb0f5ba7 100644
--- a/dumux/boxmodels/2p2cni/2p2cnivolumevariables.hh
+++ b/dumux/boxmodels/2p2cni/2p2cnivolumevariables.hh
@@ -89,7 +89,7 @@ public:
      *        the sub-control volume.
      */
     Scalar thermalConductivity(const int phaseIdx) const
-    { FluidSystem::thermalConductivity(this->fluidState_, phaseIdx); };
+    { return FluidSystem::thermalConductivity(this->fluidState_, phaseIdx); };
 
 
 protected: