diff --git a/Src/stm32l4xx_hal_usart.c b/Src/stm32l4xx_hal_usart.c
index 5a37355..c51e8ab 100644
--- a/Src/stm32l4xx_hal_usart.c
+++ b/Src/stm32l4xx_hal_usart.c
@@ -418,6 +418,8 @@
 /**
   * @brief  Register a User USART Callback
   *         To be used instead of the weak predefined callback
+  * @note   The HAL_USART_RegisterCallback() may be called before HAL_USART_Init() in HAL_USART_STATE_RESET
+  *         to register callbacks for HAL_USART_MSPINIT_CB_ID and HAL_USART_MSPDEINIT_CB_ID
   * @param  husart usart handle
   * @param  CallbackID ID of the callback to be registered
   *         This parameter can be one of the following values:
@@ -447,8 +449,6 @@
 
     return HAL_ERROR;
   }
-  /* Process locked */
-  __HAL_LOCK(husart);
 
   if (husart->State == HAL_USART_STATE_READY)
   {
@@ -539,15 +539,14 @@
     status =  HAL_ERROR;
   }
 
-  /* Release Lock */
-  __HAL_UNLOCK(husart);
-
   return status;
 }
 
 /**
   * @brief  Unregister an USART Callback
   *         USART callaback is redirected to the weak predefined callback
+  * @note   The HAL_USART_UnRegisterCallback() may be called before HAL_USART_Init() in HAL_USART_STATE_RESET
+  *         to un-register callbacks for HAL_USART_MSPINIT_CB_ID and HAL_USART_MSPDEINIT_CB_ID
   * @param  husart usart handle
   * @param  CallbackID ID of the callback to be unregistered
   *         This parameter can be one of the following values:
@@ -568,9 +567,6 @@
 {
   HAL_StatusTypeDef status = HAL_OK;
 
-  /* Process locked */
-  __HAL_LOCK(husart);
-
   if (HAL_USART_STATE_READY == husart->State)
   {
     switch (CallbackID)
@@ -660,9 +656,6 @@
     status =  HAL_ERROR;
   }
 
-  /* Release Lock */
-  __HAL_UNLOCK(husart);
-
   return status;
 }
 #endif /* USE_HAL_USART_REGISTER_CALLBACKS */