diff --git a/easypy/threadtree.py b/easypy/threadtree.py
index df97fb1..1ffbbca 100644
--- a/easypy/threadtree.py
+++ b/easypy/threadtree.py
@@ -88,19 +88,22 @@ def start_new_thread(target, *args, **kwargs):
 
     def wrapper(*args, **kwargs):
         thread = threading.current_thread()
+        child_uuid = get_thread_uuid(thread)
+        registry_key = (parent_uuid, child_uuid)
+
         if not DISABLE_ACROSS_THREADS:
-            _FRAME_SNAPSHOTS_REGISTRY[parent_thread.uuid, thread.uuid] = create_frame_snapshot(parent_frame, parent_thread)
-        uuid = get_thread_uuid(thread)
-        UUIDS_TREE[uuid] = parent_uuid
+            _FRAME_SNAPSHOTS_REGISTRY[registry_key] = create_frame_snapshot(parent_frame, parent_thread)
+
+        UUIDS_TREE[child_uuid] = parent_uuid
         if _REGISTER_GREENLETS:
             IDENT_TO_GREENLET[thread.ident] = gevent.getcurrent()
         try:
             return target(*args, **kwargs)
         finally:
             # remove the snapshot connecting parent → this thread
-            _FRAME_SNAPSHOTS_REGISTRY.pop((parent_thread.uuid, thread.uuid), None)
+            _FRAME_SNAPSHOTS_REGISTRY.pop(registry_key, None)
 
-            IDENT_TO_UUID.pop(thread.ident)
+            IDENT_TO_UUID.pop(thread.ident, None)
 
     return _orig_start_new_thread(wrapper, *args, **kwargs)