diff --git a/src/osgGA/UFOManipulator.cpp b/src/osgGA/UFOManipulator.cpp
index 669981f5c..ba0b8adbd 100644
--- a/src/osgGA/UFOManipulator.cpp
+++ b/src/osgGA/UFOManipulator.cpp
@@ -1,6 +1,10 @@
 #include <osgGA/UFOManipulator>
 #include <osgUtil/IntersectVisitor>
 
+#ifndef M_PI
+# define M_PI       3.14159265358979323846  /* pi */
+#endif
+
 using namespace osgGA;
 
 UFOManipulator::UFOManipulator():