diff --git a/src/Makefile.am b/src/Makefile.am
index 67f7cb31ecf51f5867aa545dc0474ef8c955e137..c217f9a957fbf6d1a350594c125f096f5731d409 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -6,7 +6,7 @@ noinst_PROGRAMS = \
 
 test_gradient_method_SOURCES = \
 	test-gradient-method.cc \
-	mynonlinearity.cc \
+	mynonlinearity.hh \
 	finitescalarincreasingconvexfunction.hh \
 	samplefunctional.hh
 
diff --git a/src/mynonlinearity.cc b/src/mynonlinearity.hh
similarity index 96%
rename from src/mynonlinearity.cc
rename to src/mynonlinearity.hh
index b114da2db62d4ee4838f59c5108c484eeda44db0..cd701fdc66f3ad7f3b1c16b6ca5f313bcae809b1 100644
--- a/src/mynonlinearity.cc
+++ b/src/mynonlinearity.hh
@@ -1,8 +1,7 @@
 /* -*- mode:c++; mode:semantic -*- */
 
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
+#ifndef MYNONLINEARITY_HH
+#define MYNONLINEARITY_HH
 
 #include <dune/common/fvector.hh>
 #include <dune/common/fmatrix.hh>
@@ -53,3 +52,4 @@ class MyNonlinearity {
   OuterFunction func_;
 };
 }
+#endif
diff --git a/src/samplefunctional.hh b/src/samplefunctional.hh
index fcebf5cce995ed9852d5131508b0c7f144a03922..5b479c8001d2da3199b4f6bf692262b3f7d9a356 100644
--- a/src/samplefunctional.hh
+++ b/src/samplefunctional.hh
@@ -10,7 +10,7 @@
 #include <dune/tnnmg/problem-classes/bisection.hh>
 #include <dune/tnnmg/problem-classes/directionalconvexfunction.hh>
 
-#include "mynonlinearity.cc"
+#include "mynonlinearity.hh"
 #include "finitescalarincreasingconvexfunction.hh"
 
 namespace Dune {