diff --git a/swift/Swift.py b/swift/Swift.py
index 02439b5..22819da 100644
--- a/swift/Swift.py
+++ b/swift/Swift.py
@@ -224,7 +224,9 @@ def step(self, dt=0.05, render=True):
 
         # Update world transform of objects
         for obj in self.swift_objects:
-            obj._propogate_scene_tree()
+            # check if object is deleted
+            if obj is not None:
+                obj._propogate_scene_tree()
 
         # Adjust sim time
         self.sim_time += dt