diff --git a/include/libopencm3/stm32/f0/rcc.h b/include/libopencm3/stm32/f0/rcc.h
index bca01009..ead1ba64 100644
--- a/include/libopencm3/stm32/f0/rcc.h
+++ b/include/libopencm3/stm32/f0/rcc.h
@@ -318,6 +318,9 @@ Control</b>
 /* --- RCC_CFGR2 values ---------------------------------------------------- */
 
 #define RCC_CFGR2_PREDIV			0xf
+/** @defgroup rcc_cfgr2_prediv PLL source predividers
+@ingroup rcc_defines
+@{*/
 #define RCC_CFGR2_PREDIV_NODIV			0x0
 #define RCC_CFGR2_PREDIV_DIV2			0x1
 #define RCC_CFGR2_PREDIV_DIV3			0x2
@@ -334,6 +337,7 @@ Control</b>
 #define RCC_CFGR2_PREDIV_DIV14			0xd
 #define RCC_CFGR2_PREDIV_DIV15			0xe
 #define RCC_CFGR2_PREDIV_DIV16			0xf
+/**@}*/
 
 /* --- RCC_CFGR3 values ---------------------------------------------------- */
 
diff --git a/lib/stm32/f0/rcc.c b/lib/stm32/f0/rcc.c
index 75fe6a87..b7cb6b19 100644
--- a/lib/stm32/f0/rcc.c
+++ b/lib/stm32/f0/rcc.c
@@ -483,7 +483,12 @@ void rcc_set_hpre(uint32_t hpre)
 	RCC_CFGR = (RCC_CFGR & ~RCC_CFGR_HPRE) | hpre;
 }
 
-
+/**
+ * Set PLL Source pre-divider **CAUTION**.
+ * On F03x and F05, prediv only applies to HSE source. On others, this
+ * is _after_ source selection. See also f3.
+ * @param[in] prediv division by prediv+1 @ref rcc_cfgr2_prediv
+ */
 void rcc_set_prediv(uint32_t prediv)
 {
 	RCC_CFGR2 = (RCC_CFGR2 & ~RCC_CFGR2_PREDIV) | prediv;