diff --git a/dune/tectonic/mydirectionalconvexfunction.hh b/dune/tectonic/mydirectionalconvexfunction.hh
index 41ff5bcc91f104158991b20553f64387eb1b608e..91b278da5efe6c2dc14824d3d5507eea99bd9c74 100644
--- a/dune/tectonic/mydirectionalconvexfunction.hh
+++ b/dune/tectonic/mydirectionalconvexfunction.hh
@@ -1,4 +1,5 @@
 // Copied from dune/tnnmg/problem-classes/directionalconvexfunction.hh
+// so that phi can be const
 
 #ifndef MY_DIRECTIONAL_CONVEX_FUNCTION_HH
 #define MY_DIRECTIONAL_CONVEX_FUNCTION_HH