diff --git a/src/mynonlinearity.hh b/src/mynonlinearity.hh
index e8d4fe8d5173f6c198cb2a8853a97b3e9ff507b7..b6002adfec376ebed1dc7c924c87916ec6290767 100644
--- a/src/mynonlinearity.hh
+++ b/src/mynonlinearity.hh
@@ -29,7 +29,7 @@ class MyNonlinearity {
   void directionalSubDiff(VectorType const u, VectorType const v,
                           Interval<double> &D) const {
     if (u == SmallVector(0.0)) {
-      D[0] = D[1] = func_.rightDifferential(0);
+      D[0] = D[1] = func_.rightDifferential(0) * v.two_norm();
       return;
     }
     double const un = u.two_norm();