diff --git a/libsrc/csg/solid.cpp b/libsrc/csg/solid.cpp
index 25706c2c..ab35fcbf 100644
--- a/libsrc/csg/solid.cpp
+++ b/libsrc/csg/solid.cpp
@@ -1498,7 +1498,6 @@ namespace netgen
 	}
       }
   }
-
   void Solid :: ForEachSurface (const std::function<void(Surface*,bool)> & lambda, bool inv) const
   {
     switch (op)
diff --git a/libsrc/csg/solid.hpp b/libsrc/csg/solid.hpp
index 17e03512..7fe9539d 100644
--- a/libsrc/csg/solid.hpp
+++ b/libsrc/csg/solid.hpp
@@ -7,6 +7,8 @@
 /* Date:   1. Dez. 95                                                     */
 /**************************************************************************/
 
+#include <functional>
+
 namespace netgen 
 {