diff --git a/easypost/shipment.py b/easypost/shipment.py
index 7f1f7c88..53500f3e 100644
--- a/easypost/shipment.py
+++ b/easypost/shipment.py
@@ -75,7 +75,7 @@ def lowest_rate(self, carriers: List[str] = None, services: List[str] = None) ->
     def lowest_smartrate(self, delivery_days: int, delivery_accuracy: str) -> Rate:
         """Get the lowest smartrate of this shipment."""
         smartrates = self.get_smartrates()
-        lowest_smartrate = self.get_lowest_smartrate(smartrates, delivery_days, delivery_accuracy)
+        lowest_smartrate = self.get_lowest_smartrate(smartrates, delivery_days, delivery_accuracy.lower())
 
         return lowest_smartrate