diff --git a/python-algo/gamelib/unit.py b/python-algo/gamelib/unit.py
index f573eefe..a19b391e 100644
--- a/python-algo/gamelib/unit.py
+++ b/python-algo/gamelib/unit.py
@@ -72,7 +72,7 @@ def upgrade(self):
         self.max_health = type_config.get("startHealth", self.max_health)
         self.shieldPerUnit = type_config.get("shieldPerUnit", self.shieldPerUnit)
         self.shieldBonusPerY = type_config.get("shieldBonusPerY", self.shieldBonusPerY)
-        self.cost = [type_config.get("cost1", 0) + self.cost[0], type_config.get("cost2", 0) + self.cost[1]]
+        self.cost = [type_config.get("cost1", self.cost[0]) + self.cost[0], type_config.get("cost2", self.cost[1]) + self.cost[1]]
         self.upgraded = True