diff --git a/python_payload/st3m/ui/mixer.py b/python_payload/st3m/ui/mixer.py
index 59c1696868968872ee93f5f2694baed6a1b799ed..454334f35b673ffd72f20dce738035fc647909fd 100644
--- a/python_payload/st3m/ui/mixer.py
+++ b/python_payload/st3m/ui/mixer.py
@@ -350,7 +350,9 @@ class AudioMixer(Responder):
                 shift = 0
             else:
                 shift = 7
-            ctx.rectangle(chan_width / 2 - 16 + shift, bar_bottom - len_bar, 12-shift, len_bar).fill()
+            ctx.rectangle(
+                chan_width / 2 - 16 + shift, bar_bottom - len_bar, 12 - shift, len_bar
+            ).fill()
 
             # reference notch
             ctx.move_to(chan_width / 2 - 16 + shift, bar_bottom - len_bar * 5 / 7)