diff --git a/flight/sys/pios_led.h b/flight/sys/pios_led.h
index 020fae166..2cc4c431a 100644
--- a/flight/sys/pios_led.h
+++ b/flight/sys/pios_led.h
@@ -32,9 +32,9 @@
 typedef enum {LED1 = 0, LED2 = 1} Led_TypeDef;
 
 /* Exported Functions */
-void LED_INIT(void);
-void LED_ON(Led_TypeDef LEDNum);
-void LED_OFF(Led_TypeDef LEDNum);
-void LED_TOGGLE(Led_TypeDef LEDNum);
+extern void LED_INIT(void);
+extern void LED_ON(Led_TypeDef LEDNum);
+extern void LED_OFF(Led_TypeDef LEDNum);
+extern void LED_TOGGLE(Led_TypeDef LEDNum);
 
 #endif /* PIOS_LED_H */
diff --git a/flight/sys/pios_settings.h b/flight/sys/pios_settings.h
index 512d0607b..343422c8a 100644
--- a/flight/sys/pios_settings.h
+++ b/flight/sys/pios_settings.h
@@ -61,6 +61,6 @@ typedef struct {
 extern SettingsTypeDef Settings;
 
 /* Function Prototypes */
-void LoadSettings(void);
+extern void LoadSettings(void);
 
 #endif /* PIOS_SETTINGS_H */
\ No newline at end of file
diff --git a/flight/sys/pios_sys.h b/flight/sys/pios_sys.h
index 0dc7d98fa..745bbd921 100644
--- a/flight/sys/pios_sys.h
+++ b/flight/sys/pios_sys.h
@@ -29,8 +29,8 @@
 #define PIOS_SYS_H
 
 /* Exported Functions */
-void SysInit(void);
-void GPIO_Configuration(void);
-void NVIC_Configuration(void);
+extern void SysInit(void);
+extern void GPIO_Configuration(void);
+extern void NVIC_Configuration(void);
 
 #endif /* PIOS_SYS_H */
diff --git a/flight/sys/pios_uart.h b/flight/sys/pios_uart.h
index 3975a0d5b..95030e604 100644
--- a/flight/sys/pios_uart.h
+++ b/flight/sys/pios_uart.h
@@ -29,9 +29,9 @@
 #define PIOS_UART_H
 
 /* Function Prototypes */
-void UARTInit(void);
-void EnableAuxUART(void);
-void DisableAuxUART(void);
-void UARTChangeBaud(USART_TypeDef* USARTx, uint32_t Baud);
+extern void UARTInit(void);
+extern void EnableAuxUART(void);
+extern void DisableAuxUART(void);
+extern void UARTChangeBaud(USART_TypeDef* USARTx, uint32_t Baud);
 
 #endif /* PIOS_UART_H */