diff --git a/dune/tectonic/nicefunction.hh b/dune/tectonic/nicefunction.hh
index 6f95513c5528e1e6e7ad5ee3c2bfbe7b109249e4..bf000fc85285ae86e734d7d252d0cd469e74c577 100644
--- a/dune/tectonic/nicefunction.hh
+++ b/dune/tectonic/nicefunction.hh
@@ -99,13 +99,13 @@ class RuinaFunction : public NiceFunction {
   }
 
 private:
-  double coefficient;
-  double a;
-  double mu;
-  double eta;
-  double normalStress;
+  double const coefficient;
+  double const a;
+  double const mu;
+  double const eta;
+  double const normalStress;
 
-  double rho;
+  double const rho;
 };
 
 class LinearFunction : public NiceFunction {
@@ -125,7 +125,7 @@ class LinearFunction : public NiceFunction {
   double virtual regularity(double s) const { return 0; }
 
 private:
-  double coefficient;
+  double const coefficient;
 };
 
 template <int slope> class SampleFunction : public NiceFunction {