diff --git a/targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/system_clock.c b/targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/system_clock.c
index 464494148e..b2e1661388 100644
--- a/targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/system_clock.c
+++ b/targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/system_clock.c
@@ -55,7 +55,7 @@ uint8_t SetSysClock_PLL_HSI(void);
   * @retval None
   */
 
-void SetSysClock(void)
+MBED_WEAK void SetSysClock(void)
 {
 #if ((CLOCK_SOURCE) & USE_PLL_HSE_EXTC)
     /* 1- Try to start with HSE and external clock (MCO from STLink PCB part) */
@@ -158,7 +158,7 @@ MBED_WEAK uint8_t SetSysClock_PLL_HSE(uint8_t bypass)
 /******************************************************************************/
 /*            PLL (clocked by HSI) used as System clock source                */
 /******************************************************************************/
-uint8_t SetSysClock_PLL_HSI(void)
+MBED_WEAK uint8_t SetSysClock_PLL_HSI(void)
 {
     RCC_ClkInitTypeDef RCC_ClkInitStruct;
     RCC_OscInitTypeDef RCC_OscInitStruct;