diff --git a/src/friction_writer.hh b/src/friction_writer.hh
index a4902e228d344428d045fefbc68e7970e3c9496b..97a7055f3bd7c90c04a67bac2cf20e525c6c24fc 100644
--- a/src/friction_writer.hh
+++ b/src/friction_writer.hh
@@ -1,4 +1,6 @@
-//#include <iostream>
+#ifndef FRICTION_WRITER_HH
+#define FRICTION_WRITER_HH
+
 #include <fstream>
 
 #include <dune/tectonic/frictiondata.hh>
@@ -21,3 +23,4 @@ template <class BitVectorType> class FrictionWriter {
   FrictionData const &fd;
   BitVectorType const &boundaryNodes;
 };
+#endif