diff --git a/include/osgSim/OverlayNode b/include/osgSim/OverlayNode
index 76ae9625a..42794f590 100644
--- a/include/osgSim/OverlayNode
+++ b/include/osgSim/OverlayNode
@@ -49,7 +49,7 @@ class OSGSIM_EXPORT OverlayNode : public osg::Group
 
 
         void setOverlayTechnique(OverlayTechnique technique);
-        OverlayTechnique getOverlayTechnique() { return _overlayTechnique; }
+        OverlayTechnique getOverlayTechnique() const { return _overlayTechnique; }
 
 
         /** Set the overlay subgraph which will be rendered to texture.*/