diff --git a/src/osgViewer/PixelBufferCarbon.cpp b/src/osgViewer/PixelBufferCarbon.cpp
index c995c3933..0e18de3b0 100644
--- a/src/osgViewer/PixelBufferCarbon.cpp
+++ b/src/osgViewer/PixelBufferCarbon.cpp
@@ -115,6 +115,11 @@ void  PixelBufferCarbon::closeImplementation()
     if (_pbuffer) aglDestroyPBuffer(_pbuffer);
     if (_context) aglDestroyContext(_context);
     if (_pixelformat) aglDestroyPixelFormat(_pixelformat);
+    
+    _pbuffer = NULL;
+    _context = NULL;
+    _pixelformat = NULL;
+    
     _valid = _realized = false;
 }