diff --git a/stm32/mk4-bootloader/clocks.c b/stm32/mk4-bootloader/clocks.c
index e52a4e22..10ceb9d8 100644
--- a/stm32/mk4-bootloader/clocks.c
+++ b/stm32/mk4-bootloader/clocks.c
@@ -168,7 +168,7 @@ clocks_setup(void)
     PeriphClkInitStruct.Sai1ClockSelection = RCC_SAI1CLKSOURCE_PLLSAI1;
     PeriphClkInitStruct.AdcClockSelection = RCC_ADCCLKSOURCE_PLLSAI1;
     PeriphClkInitStruct.UsbClockSelection = RCC_USBCLKSOURCE_PLLSAI1;
-    PeriphClkInitStruct.RTCClockSelection = RCC_RTCCLKSOURCE_LSE;           // XXX wrong?
+    PeriphClkInitStruct.RTCClockSelection = RCC_RTCCLKSOURCE_HSE_DIV32; // but unused
     PeriphClkInitStruct.RngClockSelection = RCC_RNGCLKSOURCE_PLLSAI1;
 
     PeriphClkInitStruct.PLLSAI1.PLLSAI1Source = RCC_PLLSOURCE_HSE;