diff --git a/dumux/multidomain/2cnistokes2p2cni/stokesncnicouplinglocalresidual.hh b/dumux/multidomain/2cnistokes2p2cni/stokesncnicouplinglocalresidual.hh
index 671ae29efa979d4db488e6a41fb3d0d408e135b9..948499aa359c902e163b35a59a5869a4e9c0d97c 100644
--- a/dumux/multidomain/2cnistokes2p2cni/stokesncnicouplinglocalresidual.hh
+++ b/dumux/multidomain/2cnistokes2p2cni/stokesncnicouplinglocalresidual.hh
@@ -158,16 +158,13 @@ public:
                     for (int compIdx = 0; compIdx < numComponents; compIdx++)
                     {
                         int eqIdx =  conti0EqIdx + compIdx;
-                        if (eqIdx != massBalanceIdx)
+                        if ((eqIdx != massBalanceIdx) && bcTypes.isCouplingDirichlet(eqIdx))
                         {
-                            if (bcTypes.isCouplingDirichlet(eqIdx))
-                            {
-                                if(useMoles)
-                                    this->residual_[scvIdx][eqIdx] = volVars.moleFraction(compIdx);
-                                else
-                                    this->residual_[scvIdx][eqIdx] = volVars.massFraction(compIdx);
-                                Valgrind::CheckDefined(this->residual_[scvIdx][compIdx]);
-                            }
+                            if(useMoles)
+                                this->residual_[scvIdx][eqIdx] = volVars.moleFraction(compIdx);
+                            else
+                                this->residual_[scvIdx][eqIdx] = volVars.massFraction(compIdx);
+                            Valgrind::CheckDefined(this->residual_[scvIdx][compIdx]);
                         }
                     }
 
diff --git a/dumux/multidomain/2cstokes2p2c/localoperator.hh b/dumux/multidomain/2cstokes2p2c/localoperator.hh
index 733d4c0f9dc9420c309e192041d52c3f54a88f0c..f43d9da119fb263b015ec0aa8bb85d596b27c0e2 100644
--- a/dumux/multidomain/2cstokes2p2c/localoperator.hh
+++ b/dumux/multidomain/2cstokes2p2c/localoperator.hh
@@ -432,6 +432,11 @@ public:
         const Scalar normalMassFlux1 = boundaryVars1.normalVelocity()
                                        * cParams.elemVolVarsCur1[vertInElem1].density();
 
+        if (std::abs(bfNormal1[1]) < 1e-10)
+        {
+            DUNE_THROW(Dune::NotImplemented, "The coupling conditions are not implemented for vertical interfaces.");
+        }
+
         // MASS Balance
         // Neumann-like conditions
         if (cParams.boundaryTypes1.isCouplingNeumann(massBalanceIdx1))
diff --git a/dumux/multidomain/2cstokes2p2c/stokesnccouplinglocalresidual.hh b/dumux/multidomain/2cstokes2p2c/stokesnccouplinglocalresidual.hh
index c32b05c77609991240852e7b351e4f74b63e4a3c..ec2f7bcf18c1effb516c2ce4c55d3ff2fb6d877e 100644
--- a/dumux/multidomain/2cstokes2p2c/stokesnccouplinglocalresidual.hh
+++ b/dumux/multidomain/2cstokes2p2c/stokesnccouplinglocalresidual.hh
@@ -168,15 +168,13 @@ public:
                     for (int compIdx = 0; compIdx < numComponents; compIdx++)
                     {
                         int eqIdx = conti0EqIdx + compIdx;
-                        if (eqIdx != massBalanceIdx)
+                        if ((eqIdx != massBalanceIdx) && bcTypes.isCouplingDirichlet(eqIdx))
                         {
-                            if (bcTypes.isCouplingDirichlet(eqIdx))
-                            {
-                                if(useMoles)
-                                    this->residual_[scvIdx][eqIdx] = volVars.moleFraction(compIdx);
-                                else
-                                    this->residual_[scvIdx][eqIdx] = volVars.massFraction(compIdx);
-                            }
+                            if (useMoles)
+                                this->residual_[scvIdx][eqIdx] = volVars.moleFraction(compIdx);
+                            else
+                                this->residual_[scvIdx][eqIdx] = volVars.massFraction(compIdx);
+                            Valgrind::CheckDefined(this->residual_[scvIdx][compIdx]);
                         }
                     }
                 }