diff --git a/pvlib/transformer.py b/pvlib/transformer.py
index 3b66b0beb3..88fa44fd63 100644
--- a/pvlib/transformer.py
+++ b/pvlib/transformer.py
@@ -105,6 +105,9 @@ def simple_efficiency(
        pg. 101.
     '''  # noqa: E501
 
+    if load_loss == 0:
+        return input_power - no_load_loss * transformer_rating
+
     input_power_normalized = input_power / transformer_rating
 
     a = load_loss