diff --git a/opm/core/utility/VelocityInterpolation.cpp b/opm/core/utility/VelocityInterpolation.cpp
index c8678898..fe1514af 100644
--- a/opm/core/utility/VelocityInterpolation.cpp
+++ b/opm/core/utility/VelocityInterpolation.cpp
@@ -73,6 +73,7 @@ namespace Opm
             if (cell == grid_.face_cells[2*face]) {
                 face_flux = flux_[face];
             } else {
+                ASSERT(cell == grid_.face_cells[2*face + 1]);
                 face_flux = -flux_[face];
             }
             for (int dd = 0; dd < dim; ++dd) {
diff --git a/tests/test_velocityinterpolation.cpp b/tests/test_velocityinterpolation.cpp
index 372868ea..2e7f9aa1 100644
--- a/tests/test_velocityinterpolation.cpp
+++ b/tests/test_velocityinterpolation.cpp
@@ -465,7 +465,7 @@ BOOST_AUTO_TEST_CASE(test_VelocityInterpolationConstant)
     testConstantVelRepro2d<VelocityInterpolationConstant>();
     testConstantVelReproPyramid<VelocityInterpolationConstant>();
     testConstantVelReproIrreg2d<VelocityInterpolationConstant>();
-    // testConstantVelReproIrregPrism<VelocityInterpolationConstant>(); // We should verify if this is expected to fail or not.
+    testConstantVelReproIrregPrism<VelocityInterpolationConstant>();
 }
 
 BOOST_AUTO_TEST_CASE(test_VelocityInterpolationECVI)