diff --git a/src/STM32RTC.h b/src/STM32RTC.h
index b4de135..9a5449e 100644
--- a/src/STM32RTC.h
+++ b/src/STM32RTC.h
@@ -188,7 +188,7 @@ class STM32RTC {
   friend class STM32LowPower;
 
 private:
-  STM32RTC(void): _clockSource(RTC_LSI_CLOCK) {}
+  STM32RTC(void): _clockSource(RTC_LSE_CLOCK) {}
 
   static bool _configured;