diff --git a/modules/production/production.py b/modules/production/production.py
index cf20bf714f..650e4accb4 100644
--- a/modules/production/production.py
+++ b/modules/production/production.py
@@ -305,8 +305,7 @@ class Production(ShipmentAssignMixin, Workflow, ModelSQL, ModelView):
 
     @fields.depends('product', 'bom')
     def compute_lead_time(self, pattern=None):
-        if pattern is None:
-            pattern = {}
+        pattern = pattern.copy() if pattern is not None else {}
         if self.product:
             pattern.setdefault('bom', self.bom.id if self.bom else None)
             for line in self.product.production_lead_times:
diff --git a/modules/production_routing/production.py b/modules/production_routing/production.py
index 4eff9953b7..00e77cec9c 100644
--- a/modules/production_routing/production.py
+++ b/modules/production_routing/production.py
@@ -28,8 +28,7 @@ class Production(metaclass=PoolMeta):
 
     @fields.depends('routing')
     def on_change_with_planned_start_date(self, pattern=None):
-        if pattern is None:
-            pattern = {}
+        pattern = pattern.copy() if pattern is not None else {}
         pattern.setdefault(
             'routing', self.routing.id if self.routing else None)
         return super(Production, self).on_change_with_planned_start_date(