diff --git a/panda/src/display/graphicsEngine.h b/panda/src/display/graphicsEngine.h
index 51f0eae5b8..8b2b4922c0 100644
--- a/panda/src/display/graphicsEngine.h
+++ b/panda/src/display/graphicsEngine.h
@@ -75,7 +75,7 @@ PUBLISHED:
   INLINE PT(GraphicsStateGuardian) make_gsg(GraphicsPipe *pipe);
   PT(GraphicsStateGuardian) make_gsg(GraphicsPipe *pipe,
                                      const FrameBufferProperties &properties,
-                                     GraphicsStateGuardian *share_with);
+                                     GraphicsStateGuardian *share_with = NULL);
 
   GraphicsWindow *make_window(GraphicsStateGuardian *gsg, const string &name,
                               int sort);