diff --git a/src/main.c b/src/main.c
index 5d9f25d..607f6c1 100644
--- a/src/main.c
+++ b/src/main.c
@@ -44,17 +44,17 @@ THE SOFTWARE.
 #include "util.h"
 
 void HAL_MspInit(void);
-void SystemClock_Config(void);
+static void SystemClock_Config(void);
 static bool send_to_host_or_enqueue(struct gs_host_frame *frame);
 static void send_to_host(void);
 
-can_data_t hCAN = {0};
-USBD_HandleTypeDef hUSB = {0};
-led_data_t hLED = {0};
+static can_data_t hCAN = {0};
+static USBD_HandleTypeDef hUSB = {0};
+static led_data_t hLED = {0};
 
-queue_t *q_frame_pool = NULL;
-queue_t *q_from_host = NULL;
-queue_t *q_to_host = NULL;
+static queue_t *q_frame_pool = NULL;
+static queue_t *q_from_host = NULL;
+static queue_t *q_to_host = NULL;
 
 int main(void)
 {
diff --git a/src/usbd_desc.c b/src/usbd_desc.c
index f67c962..fcdda71 100644
--- a/src/usbd_desc.c
+++ b/src/usbd_desc.c
@@ -30,13 +30,13 @@ THE SOFTWARE.
 #include "config.h"
 #include "util.h"
 
-uint8_t *USBD_FS_DeviceDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
-uint8_t *USBD_FS_LangIDStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
-uint8_t *USBD_FS_ManufacturerStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
-uint8_t *USBD_FS_ProductStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
-uint8_t *USBD_FS_SerialStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
-uint8_t *USBD_FS_ConfigStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
-uint8_t *USBD_FS_InterfaceStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
+static uint8_t *USBD_FS_DeviceDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
+static uint8_t *USBD_FS_LangIDStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
+static uint8_t *USBD_FS_ManufacturerStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
+static uint8_t *USBD_FS_ProductStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
+static uint8_t *USBD_FS_SerialStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
+static uint8_t *USBD_FS_ConfigStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
+static uint8_t *USBD_FS_InterfaceStrDescriptor(USBD_SpeedTypeDef speed, uint16_t *length);
 
 #ifdef USB_SUPPORT_USER_STRING_DESC
 uint8_t *USBD_FS_USRStringDesc(USBD_SpeedTypeDef speed, uint8_t idx, uint16_t *length);