diff --git a/modules/production/stock.py b/modules/production/stock.py
index c81e8e83ff..9ef1025a28 100644
--- a/modules/production/stock.py
+++ b/modules/production/stock.py
@@ -206,13 +206,15 @@ class LotTrace(metaclass=PoolMeta):
             else_=document)
 
     def _get_upward_traces(self):
-        traces = super()._get_upward_traces()
         if self.production_input:
-            traces.update(self.production_input.outputs)
+            traces = set(self.production_input.outputs)
+        else:
+            traces = super()._get_upward_traces()
         return traces
 
     def _get_downward_traces(self):
-        traces = super()._get_downward_traces()
         if self.production_output:
-            traces.update(self.production_output.inputs)
+            traces = set(self.production_output.inputs)
+        else:
+            traces = super()._get_downward_traces()
         return traces