diff --git a/highway_env/vehicle/behavior.py b/highway_env/vehicle/behavior.py
index 1ac8babea..7378f63b8 100644
--- a/highway_env/vehicle/behavior.py
+++ b/highway_env/vehicle/behavior.py
@@ -451,7 +451,10 @@ def acceleration_features(
     ) -> np.ndarray:
         vt, dv, dp = 0, 0, 0
         if ego_vehicle:
-            vt = getattr(ego_vehicle, "target_speed", ego_vehicle.speed) - ego_vehicle.speed
+            vt = (
+                getattr(ego_vehicle, "target_speed", ego_vehicle.speed)
+                - ego_vehicle.speed
+            )
             d_safe = (
                 self.DISTANCE_WANTED
                 + np.maximum(ego_vehicle.speed, 0) * self.TIME_WANTED