diff --git a/direct/src/distributed/DistributedCartesianGrid.py b/direct/src/distributed/DistributedCartesianGrid.py
index d1a67cbb09..2ce973fff3 100755
--- a/direct/src/distributed/DistributedCartesianGrid.py
+++ b/direct/src/distributed/DistributedCartesianGrid.py
@@ -69,6 +69,7 @@ class DistributedCartesianGrid(DistributedNode, CartesianGridBase):
         return self.centerPos
 
     def startProcessVisibility(self, avatar):
+        assert not self.cr._noNewInterests
         self.stopProcessVisibility()
         self.visAvatar = avatar
         self.visZone = None