diff --git a/targets/TARGET_STM/TARGET_STM32F4/TARGET_STM32F412xG/system_clock.c b/targets/TARGET_STM/TARGET_STM32F4/TARGET_STM32F412xG/system_clock.c
index 3f0f28f220d..6d75fda249e 100644
--- a/targets/TARGET_STM/TARGET_STM32F4/TARGET_STM32F412xG/system_clock.c
+++ b/targets/TARGET_STM/TARGET_STM32F4/TARGET_STM32F412xG/system_clock.c
@@ -88,7 +88,7 @@ void SetSysClock(void)
 /******************************************************************************/
 /*            PLL (clocked by HSE) used as System clock source                */
 /******************************************************************************/
-uint8_t SetSysClock_PLL_HSE(uint8_t bypass)
+MBED_WEAK uint8_t SetSysClock_PLL_HSE(uint8_t bypass)
 {
     RCC_OscInitTypeDef RCC_OscInitStruct;
     RCC_ClkInitTypeDef RCC_ClkInitStruct;