diff --git a/libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp b/libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp
index fc2239f823..e384357d60 100644
--- a/libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp
+++ b/libraries/AP_HAL_ChibiOS/HAL_ChibiOS_Class.cpp
@@ -109,8 +109,11 @@ static THD_FUNCTION(main_loop,arg)
 {
     daemon_task = chThdGetSelfX();
 
-    //Clear all I2C Buses
+#ifdef HAL_I2C_CLEAR_BUS
+    // Clear all I2C Buses. This can be needed on some boards which
+    // can get a stuck I2C peripheral on boot
     ChibiOS::I2CBus::clear_all();
+#endif
 
     ChibiOS::Shared_DMA::init();
     
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/skyviper-f412/hwdef.dat b/libraries/AP_HAL_ChibiOS/hwdef/skyviper-f412/hwdef.dat
index 38bde5aba4..ea0bad5354 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/skyviper-f412/hwdef.dat
+++ b/libraries/AP_HAL_ChibiOS/hwdef/skyviper-f412/hwdef.dat
@@ -133,3 +133,6 @@ define HAL_BARO_DEFAULT HAL_BARO_20789_I2C_I2C
 define HAL_BARO_20789_I2C_BUS           1
 define HAL_BARO_20789_I2C_ADDR_PRESS 0x63
 define HAL_BARO_20789_I2C_ADDR_ICM   0x68
+
+# unstick 20789 on I2C on boot
+define HAL_I2C_CLEAR_BUS