diff --git a/dune/tectonic/nicefunction.hh b/dune/tectonic/nicefunction.hh
index 83ae7def1102c9c677d2ee9ac849aa24c5a19615..626c59e60a027448dd7ae033bc1007cd36d5b3fa 100644
--- a/dune/tectonic/nicefunction.hh
+++ b/dune/tectonic/nicefunction.hh
@@ -81,12 +81,7 @@ class RuinaFunction : public NiceFunction {
 
   /* see above */
   double virtual rightDifferential(double s) const {
-    double const arg = eta * s / h;
-    if (arg <= rho)
-      return 0;
-
-    return coefficient * normalStress *
-           (a * std::log(arg) + mu + compound_state);
+    return leftDifferential(s);
   }
 
   /*