diff --git a/klippy/extras/temperature_fan.py b/klippy/extras/temperature_fan.py
index f6613043a..9dce8c702 100644
--- a/klippy/extras/temperature_fan.py
+++ b/klippy/extras/temperature_fan.py
@@ -303,7 +303,7 @@ def __init__(self, temperature_fan, config, controlled_fan=None):
         self.last_temp = 0.0
 
     def temperature_callback(self, read_time, temp):
-        def _interpolate(sbelow, above, temp):
+        def _interpolate(below, above, temp):
             return (
                 (below[1] * (above[0] - temp)) + (above[1] * (temp - below[0]))
             ) / (above[0] - below[0])