diff --git a/src/mpu6000.c b/src/mpu6000.c
index 0ec3f4b..55b4837 100644
--- a/src/mpu6000.c
+++ b/src/mpu6000.c
@@ -68,8 +68,10 @@ void mpu6000_calibrate(void) {
         sum_gy += raw.gy;
         sum_gz += raw.gz;
         HAL_Delay(1);
-        /* Refresh IWDG every 40ms — safe during re-cal with watchdog running */
-        if (i % 40 == 39) safety_refresh();
+        /* Refresh IWDG every 40ms, starting immediately (i=0) — the gap between
+         * safety_refresh() at the top of the main loop and entry here can be
+         * ~10ms, so we must refresh on i=0 to avoid the 50ms IWDG window. */
+        if (i % 40 == 0) safety_refresh();
     }
 
     s_bias_gx = (float)sum_gx / GYRO_CAL_SAMPLES;