diff --git a/klippy/extras/pid_calibrate.py b/klippy/extras/pid_calibrate.py
index a7768e57..a00f0a1b 100644
--- a/klippy/extras/pid_calibrate.py
+++ b/klippy/extras/pid_calibrate.py
@@ -130,7 +130,7 @@ class ControlAutoTune:
     def calc_final_pid(self):
         cycle_times = [(self.peaks[pos][1] - self.peaks[pos-2][1], pos)
                        for pos in range(4, len(self.peaks))]
-        midpoint_pos = sorted(cycle_times)[len(cycle_times)/2][1]
+        midpoint_pos = sorted(cycle_times)[len(cycle_times)//2][1]
         return self.calc_pid(midpoint_pos)
     # Offline analysis helper
     def write_file(self, filename):