diff --git a/dune/gdt/timestepper/explicit-rungekutta.hh b/dune/gdt/timestepper/explicit-rungekutta.hh
index 8921ec176c0bef57a42cfc1bec6335b5482dca99..895d09a147867deb23dfb06d9e09b939a76d318b 100644
--- a/dune/gdt/timestepper/explicit-rungekutta.hh
+++ b/dune/gdt/timestepper/explicit-rungekutta.hh
@@ -200,7 +200,7 @@ public:
    * \param c Coefficients for time steps (only provide if you use ExplicitRungeKuttaMethods::other)
    */
   ExplicitRungeKuttaTimeStepper(const OperatorType& op,
-                                const DiscreteFunctionType& initial_values,
+                                DiscreteFunctionType& initial_values,
                                 const RangeFieldType r = 1.0,
                                 const double t_0 = 0.0,
                                 const MatrixType& A = ButcherArrayProviderType::A(),
diff --git a/dune/gdt/timestepper/interface.hh b/dune/gdt/timestepper/interface.hh
index 68b842687ce2c63fd6864440208d6ef238addc36..da27b26268ae92e5456f6211b89087e25dc35147 100644
--- a/dune/gdt/timestepper/interface.hh
+++ b/dune/gdt/timestepper/interface.hh
@@ -66,7 +66,7 @@ private:
           SolutionStorageProviderType;
 
 protected:
-  TimeStepperInterface(const RangeFieldType t_0, const DiscreteFunctionType& initial_values)
+  TimeStepperInterface(const RangeFieldType t_0, DiscreteFunctionType& initial_values)
     : CurrentSolutionStorageProviderType(initial_values)
     , SolutionStorageProviderType(new SolutionType())
     , t_(t_0)