diff --git a/src/nicefunction.hh b/src/nicefunction.hh
index 4500871d0f44dbd9d3a7afea67b461d7a2b938a9..432ca89a6d8384f7b2fd3c21f78ed36bbc1573ae 100644
--- a/src/nicefunction.hh
+++ b/src/nicefunction.hh
@@ -16,7 +16,7 @@ class NiceFunction : public VirtualFunction<double, double> {
 
 class Identity : public NiceFunction {
 public:
-  void virtual evaluate(const double& x, double& y) const { y = x; }
+  void virtual evaluate(double const& x, double& y) const { y = x; }
 
   double virtual leftDifferential(double s) const { return 1; }
 
@@ -25,7 +25,7 @@ class Identity : public NiceFunction {
 
 class SampleFunction : public NiceFunction {
 public:
-  void virtual evaluate(const double& x, double& y) const {
+  void virtual evaluate(double const& x, double& y) const {
     y = (x < 1) ? x : (2 * x - 1);
   }
 
@@ -36,7 +36,7 @@ class SampleFunction : public NiceFunction {
 
 class TrivialFunction : public NiceFunction {
 public:
-  void virtual evaluate(const double& x, double& y) const { y = 0; }
+  void virtual evaluate(double const& x, double& y) const { y = 0; }
 
   double virtual leftDifferential(const double) const { return 0; }
 
@@ -46,7 +46,7 @@ class TrivialFunction : public NiceFunction {
 // slope in [n-1,n] is n
 class HorribleFunction : public NiceFunction {
 public:
-  void virtual evaluate(const double& x, double& y) const {
+  void virtual evaluate(double const& x, double& y) const {
     double const fl = floor(x);
     double const sum = fl * (fl + 1) / 2;
     y = sum + (fl + 1) * (x - fl);
@@ -72,7 +72,7 @@ class HorribleFunction : public NiceFunction {
 // slope in [n-1,n] is log(n+1)
 class HorribleFunctionLogarithmic : public NiceFunction {
 public:
-  void virtual evaluate(const double& x, double& y) const {
+  void virtual evaluate(double const& x, double& y) const {
     y = 0;
     size_t const fl = floor(x);
     for (size_t i = 1; i <= fl;)