diff --git a/include/osg/Viewport b/include/osg/Viewport
index ef7d79c3c..675abd846 100644
--- a/include/osg/Viewport
+++ b/include/osg/Viewport
@@ -101,7 +101,7 @@ class OSG_EXPORT Viewport : public StateAttribute
         */
         inline const osg::Matrix computeWindowMatrix() const
         {
-            return osg::Matrix::translate(1.0f,1.0f,1.0f)*osg::Matrix::scale(0.5f*width(),0.5f*height(),0.5f);
+            return osg::Matrix::translate(1.0f,1.0f,1.0f)*osg::Matrix::scale(0.5f*width(),0.5f*height(),0.5f)*osg::Matrix::translate(x(),y(),0.0f);
         }
 
         virtual void apply(State& state) const;