diff --git a/simgear/scene/tgdb/ReaderWriterSTG.hxx b/simgear/scene/tgdb/ReaderWriterSTG.hxx
index 19a1e7ea..74b6c77b 100644
--- a/simgear/scene/tgdb/ReaderWriterSTG.hxx
+++ b/simgear/scene/tgdb/ReaderWriterSTG.hxx
@@ -22,6 +22,8 @@
 #ifndef _READERWRITERSTG_HXX
 #define _READERWRITERSTG_HXX
 
+#include <functional>
+
 #include <osgDB/ReaderWriter>
 #include <simgear/math/sg_types.hxx>