diff --git a/dumux/discretization/facecentered/staggered/geometryhelper.hh b/dumux/discretization/facecentered/staggered/geometryhelper.hh
index 1875c2256840c0253877a0e1faa453f27eab1e2e..80bb2433f5c055adcdfe8065dd93267c12aeb127 100644
--- a/dumux/discretization/facecentered/staggered/geometryhelper.hh
+++ b/dumux/discretization/facecentered/staggered/geometryhelper.hh
@@ -147,7 +147,7 @@ public:
     }
 
     //! Returns an element's facet based on the local facet index.
-    Facet facet(const SmallLocalIndexType localFacetIdx, const Element& element) const
+    static Facet facet(const SmallLocalIndexType localFacetIdx, const Element& element)
     {
         return element.template subEntity <1> (localFacetIdx);
     }
diff --git a/dumux/freeflow/navierstokes/momentum/fluxhelper.hh b/dumux/freeflow/navierstokes/momentum/fluxhelper.hh
index 0382053f9f29a882d1e08439032bee6fde3e26df..7a023de98d7d18dfddf5a5d54747345108aec2ff 100644
--- a/dumux/freeflow/navierstokes/momentum/fluxhelper.hh
+++ b/dumux/freeflow/navierstokes/momentum/fluxhelper.hh
@@ -155,16 +155,7 @@ struct NavierStokesMomentumBoundaryFluxHelper
                 if (scv.boundary())
                 {
                     const auto innerVelocity = elemVolVars[scvf.insideScvIdx()].velocity();
-                    const auto outerVelocity = [&]
-                    {
-                        if (scvf.boundary())
-                        {
-                            assert(problem.boundaryTypes(element, scvf).isDirichlet(scv.dofAxis()));
-                            return problem.dirichlet(element, scvf)[scv.dofAxis()];
-                        }
-                        else
-                            return elemVolVars[scvf.outsideScvIdx()].velocity();
-                    }();
+                    const auto outerVelocity = elemVolVars[scvf.outsideScvIdx()].velocity();
 
                     const auto rho = problem.insideAndOutsideDensity(element, fvGeometry, scvf);
                     const bool selfIsUpstream = scvf.directionSign() == sign(transportingVelocity);
diff --git a/dumux/freeflow/navierstokes/momentum/fluxvariables.hh b/dumux/freeflow/navierstokes/momentum/fluxvariables.hh
index 815dcd88e02ea84f7d9ac5288164947e70dfab97..765620d2fe55aee919111fe35cfd917e865e48b3 100644
--- a/dumux/freeflow/navierstokes/momentum/fluxvariables.hh
+++ b/dumux/freeflow/navierstokes/momentum/fluxvariables.hh
@@ -428,6 +428,8 @@ public:
             {
                 if (const auto& scv = fvGeometry.scv(scvf.insideScvIdx()); this->elemBcTypes()[scvf.localIndex()].isDirichlet(scv.dofAxis()))
                     return problem.dirichlet(this->element(), scvf)[scv.dofAxis()] * this->problem().density(this->element(), scv);
+                else
+                    DUNE_THROW(Dune::InvalidStateException, "Neither Dirichlet nor Neumann BC set at " << scvf.ipGlobal());
             }
 
             const bool selfIsUpstream = scvf.directionSign() == sign(transportingVelocity);