diff --git a/superset/utils/migrate_viz.py b/superset/utils/migrate_viz.py
index d505fb5fe7d70..6e59f1257fcbb 100644
--- a/superset/utils/migrate_viz.py
+++ b/superset/utils/migrate_viz.py
@@ -121,11 +121,11 @@ def _pre_action(self) -> None:
             self.data["contributionMode"] = "row"
 
         stacked = self.data.get("stacked_style")
-        stacked_map = {
-            "expand": "Expand",
-            "stack": "Stack",
-        }
         if stacked:
+            stacked_map = {
+                "expand": "Expand",
+                "stack": "Stack",
+            }
             self.data["show_extra_controls"] = True
             self.data["stack"] = stacked_map.get(stacked)