diff --git a/include/libopencm3/stm32/pwr.h b/include/libopencm3/stm32/pwr.h
index e5b98042..704ff369 100644
--- a/include/libopencm3/stm32/pwr.h
+++ b/include/libopencm3/stm32/pwr.h
@@ -33,6 +33,8 @@
 
 /* --- PWR_CR values ------------------------------------------------------- */
 
+/* Bits [31:9]: Reserved, must be kept at reset value. */
+
 /* DBP: Disable backup domain write protection */
 #define PWR_CR_DBP			(1 << 8)
 
@@ -64,9 +66,13 @@
 
 /* --- PWR_CSR values ------------------------------------------------------ */
 
+/* Bits [31:9]: Reserved, must be kept at reset value. */
+
 /* EWUP: Enable WKUP pin */
 #define PWR_CSR_EWUP			(1 << 8)
 
+/* Bits [7:3]: Reserved, must be kept at reset value. */
+
 /* PVDO: PVD output */
 #define PWR_CSR_PVDO			(1 << 2)
 
@@ -78,4 +84,6 @@
 
 /* --- PWR function prototypes ------------------------------------------- */
 
+/* TODO */
+
 #endif