diff --git a/arch/arm/src/stm32/stm32_pwr.c b/arch/arm/src/stm32/stm32_pwr.c
index 7973f2494dc..5eda6c08ccc 100644
--- a/arch/arm/src/stm32/stm32_pwr.c
+++ b/arch/arm/src/stm32/stm32_pwr.c
@@ -91,7 +91,7 @@ static inline void stm32_pwr_modifyreg(uint8_t offset, uint16_t clearbits, uint1
  *   writable - True: enable ability to write to backup domain registers
  *
  * Returned Value:
- *   True: The backup domain was previously writable.
+ *   None
  *
  ************************************************************************************/
 
diff --git a/arch/arm/src/stm32/stm32_pwr.h b/arch/arm/src/stm32/stm32_pwr.h
index 691acfa7a36..344834c0678 100644
--- a/arch/arm/src/stm32/stm32_pwr.h
+++ b/arch/arm/src/stm32/stm32_pwr.h
@@ -73,11 +73,15 @@ extern "C"
  *   Enables access to the backup domain (RTC registers, RTC backup data registers
  *   and backup SRAM).
  *
+ *   NOTE: Reference counting is used in order to supported nested calls to this
+ *   function.  As a consequence, every call to stm32_pwr_enablebkp(true) must
+ *   be followed by a matching call to stm32_pwr_enablebkp(false).
+ *
  * Input Parameters:
  *   writable - True: enable ability to write to backup domain registers
  *
  * Returned Value:
- *   True: The backup domain was previously writable.
+ *   None
  *
  ************************************************************************************/