diff --git a/rally.py b/rally.py
index bdb08ce..b7f4757 100644
--- a/rally.py
+++ b/rally.py
@@ -26,6 +26,7 @@ SLEEP_TIME = 1 / UPDATE_RATE
 BASE_THROTTLE = 0.9  # Base throttle for both motors
 Kp_sync = 0.05  # Proportional gain for sync correction
 Kd_sync = 0.001
+prev_error = 0
 
 # Create a digitalinout object for the user switch
 user_sw = digitalio.DigitalInOut(board.USER_SW)