diff --git a/src/samplefunctional.hh b/src/samplefunctional.hh
index df53c3fdbb2e5e38325c062cf0388a4adfaea3ad..1e01e90cc7565756954156482049117e91e601b7 100644
--- a/src/samplefunctional.hh
+++ b/src/samplefunctional.hh
@@ -5,6 +5,8 @@
 
 #include <dune/common/stdstreams.hh>
 
+#include <dune/fufem/interval.hh>
+
 #include <dune/tnnmg/problem-classes/bisection.hh>
 #include <dune/tnnmg/problem-classes/directionalconvexfunction.hh>