diff --git a/arch/arm/src/stm32/stm32_rcc.h b/arch/arm/src/stm32/stm32_rcc.h
index 6f73405398..01103fcac4 100644
--- a/arch/arm/src/stm32/stm32_rcc.h
+++ b/arch/arm/src/stm32/stm32_rcc.h
@@ -64,7 +64,8 @@
 #undef EXTERN
 #if defined(__cplusplus)
 #define EXTERN extern "C"
-extern "C" {
+extern "C"
+{
 #else
 #define EXTERN extern
 #endif
@@ -208,7 +209,20 @@ static inline void stm32_mco2config(uint32_t source, uint32_t div)
  *
  ************************************************************************************/
 
-EXTERN void stm32_clockconfig(void);
+void stm32_clockconfig(void);
+
+/************************************************************************************
+ * Name: stm32_board_clockconfig
+ *
+ * Description:
+ *   Any STM32 board may replace the "standard" board clock configuration logic with
+ *   its own, custom clock cofiguration logic.
+ *
+ ************************************************************************************/
+
+#ifdef CONFIG_ARCH_BOARD_STM32_CUSTOM_CLOCKCONFIG
+void stm32_board_clockconfig(void);
+#endif
 
 /************************************************************************************
  * Name: stm32_clockenable
@@ -236,7 +250,7 @@ EXTERN void stm32_clockconfig(void);
  ************************************************************************************/
 
 #ifdef CONFIG_PM
-EXTERN void stm32_clockenable(void);
+void stm32_clockenable(void);
 #endif
 
 /************************************************************************************
@@ -254,7 +268,7 @@ EXTERN void stm32_clockenable(void);
  *
  ************************************************************************************/
 
-EXTERN void stm32_rcc_enablelse(void);
+void stm32_rcc_enablelse(void);
 
 /****************************************************************************
  * Name: stm32_rcc_enablelsi
@@ -264,7 +278,7 @@ EXTERN void stm32_rcc_enablelse(void);
  *
  ****************************************************************************/
 
-EXTERN void stm32_rcc_enablelsi(void);
+void stm32_rcc_enablelsi(void);
 
 #undef EXTERN
 #if defined(__cplusplus)
diff --git a/arch/arm/src/stm32/stm32_rng.c b/arch/arm/src/stm32/stm32_rng.c
index 38e8108fee..5a43bb5128 100644
--- a/arch/arm/src/stm32/stm32_rng.c
+++ b/arch/arm/src/stm32/stm32_rng.c
@@ -38,8 +38,9 @@
  ****************************************************************************/
 
 #include <stdint.h>
-#include <stdio.h>
 #include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
 #include <debug.h>
 #include <errno.h>
 
diff --git a/arch/arm/src/stm32/stm32_serial.c b/arch/arm/src/stm32/stm32_serial.c
index 4594c187e8..4b5a9622a5 100644
--- a/arch/arm/src/stm32/stm32_serial.c
+++ b/arch/arm/src/stm32/stm32_serial.c
@@ -1612,8 +1612,10 @@ static int up_interrupt_common(struct up_dev_s *priv)
 
 static int up_ioctl(struct file *filep, int cmd, unsigned long arg)
 {
+#if defined(CONFIG_SERIAL_TERMIOS) || defined(CONFIG_SERIAL_TIOCSERGSTRUCT)
   struct inode      *inode = filep->f_inode;
   struct uart_dev_s *dev   = inode->i_private;
+#endif
 #ifdef CONFIG_SERIAL_TERMIOS
   struct up_dev_s   *priv  = (struct up_dev_s*)dev->priv;
 #endif