diff --git a/dune/tectonic/nicefunction.hh b/dune/tectonic/nicefunction.hh
index 575b473e0448262078db675dbfc95759d73326f6..5ceb6088a2706219d81c69c93c55a8e065fbf379 100644
--- a/dune/tectonic/nicefunction.hh
+++ b/dune/tectonic/nicefunction.hh
@@ -12,8 +12,8 @@ class NiceFunction : public VirtualFunction<double, double> {
 public:
   virtual ~NiceFunction() {}
 
-  virtual double leftDifferential(double s) const = 0;
-  virtual double rightDifferential(double s) const = 0;
+  double virtual leftDifferential(double s) const = 0;
+  double virtual rightDifferential(double s) const = 0;
 
   double virtual second_deriv(double x) const {
     DUNE_THROW(NotImplemented, "second derivative not implemented");