diff --git a/src/osgSim/Impostor.cpp b/src/osgSim/Impostor.cpp
index 3ef5a2989..284aaca08 100644
--- a/src/osgSim/Impostor.cpp
+++ b/src/osgSim/Impostor.cpp
@@ -14,6 +14,7 @@
 
 #include <algorithm>
 
+using namespace osg;
 using namespace osgSim;
 
 Impostor::Impostor()