diff --git a/testhal/STM32F1xx/EXT_WAKEUP/main.c b/testhal/STM32F1xx/EXT_WAKEUP/main.c
index 23c208873..f12a54207 100644
--- a/testhal/STM32F1xx/EXT_WAKEUP/main.c
+++ b/testhal/STM32F1xx/EXT_WAKEUP/main.c
@@ -32,7 +32,7 @@ static void extcb2(EXTDriver *extp, expchannel_t channel) {
   (void)channel;
 
   chSysLockFromIsr();
-  /* we MUST reinit clocks after waking up*/
+  /* we MUST reinit clocks after waking up if use HSE or HSI+PLL */
   stm32_clock_init();
 
   extChannelDisableI(&EXTD1, 10);