diff --git a/metaflow/plugins/pypi/conda_decorator.py b/metaflow/plugins/pypi/conda_decorator.py
index 0f7208cd76a..b1b7ee833d9 100644
--- a/metaflow/plugins/pypi/conda_decorator.py
+++ b/metaflow/plugins/pypi/conda_decorator.py
@@ -89,9 +89,10 @@ def step_init(self, flow, graph, step, decos, environment, flow_datastore, logge
                 **super_attributes["packages"],
                 **self.attributes["packages"],
             }
-            self._attributes_with_user_values = self._attributes_with_user_values.union(
+            self._attributes_with_user_values.update(
                 conda_base._attributes_with_user_values
             )
+
             self.attributes["python"] = (
                 self.attributes["python"] or super_attributes["python"]
             )
diff --git a/metaflow/plugins/pypi/pypi_decorator.py b/metaflow/plugins/pypi/pypi_decorator.py
index 69422468646..bcc7dda891a 100644
--- a/metaflow/plugins/pypi/pypi_decorator.py
+++ b/metaflow/plugins/pypi/pypi_decorator.py
@@ -43,7 +43,7 @@ def step_init(self, flow, graph, step, decos, environment, flow_datastore, logge
         if "pypi_base" in self.flow._flow_decorators:
             pypi_base = self.flow._flow_decorators["pypi_base"][0]
             super_attributes = pypi_base.attributes
-            self._attributes_with_user_values = self._attributes_with_user_values.union(
+            self._attributes_with_user_values.update(
                 pypi_base._attributes_with_user_values
             )
             self.attributes["packages"] = {