diff --git a/simgear/structure/StateMachine.cxx b/simgear/structure/StateMachine.cxx
index 76a00b29..21dff7e3 100644
--- a/simgear/structure/StateMachine.cxx
+++ b/simgear/structure/StateMachine.cxx
@@ -25,6 +25,7 @@
      
 #include "StateMachine.hxx"
 
+#include <algorithm>
 #include <cassert>
 #include <set>
 #include <boost/foreach.hpp>