diff --git a/dumux/discretization/cellcentered/mpfa/interactionvolume.hh b/dumux/discretization/cellcentered/mpfa/interactionvolume.hh
index 8d8f233b95d10045126e4b55e0c4542659f85c19..729fe9ed949c14f15a2f3729836ef262f7b4e05c 100644
--- a/dumux/discretization/cellcentered/mpfa/interactionvolume.hh
+++ b/dumux/discretization/cellcentered/mpfa/interactionvolume.hh
@@ -29,8 +29,7 @@ namespace Dumux
 {
 // forward declaration of the base class
 template<class TypeTag, MpfaMethods MpfaMethod>
-class CCMpfaInteractionVolumeImplementation
-{};
+class CCMpfaInteractionVolumeImplementation;
 
 /*!
  * \ingroup Mpfa