diff --git a/board/bootstub.c b/board/bootstub.c
index 691d0d02e33cda..626ede4870931d 100644
--- a/board/bootstub.c
+++ b/board/bootstub.c
@@ -13,8 +13,13 @@
 #endif
 
 // default since there's no serial
-void puts(const char *a) {}
-void puth(unsigned int i) {}
+void puts(const char *a) {
+ UNUSED(a);
+}
+
+void puth(unsigned int i) {
+UNUSED(i);
+}
 
 #include "libc.h"
 #include "provision.h"
@@ -34,11 +39,11 @@ void puth(unsigned int i) {}
 
 #include "spi_flasher.h"
 
-void __initialize_hardware_early() {
+void __initialize_hardware_early(void) {
   early();
 }
 
-void fail() {
+void fail(void) {
   soft_flasher_start();
 }
 
@@ -48,7 +53,7 @@ extern void *_app_start[];
 // FIXME: sometimes your panda will fail flashing and will quickly blink a single Green LED
 // BOUNTY: $200 coupon on shop.comma.ai or $100 check.
 
-int main() {
+int main(void) {
   __disable_irq();
   clock_init();
   detect();
@@ -88,7 +93,7 @@ int main() {
   return 0;
 good:
   // jump to flash
-  ((void(*)()) _app_start[1])();
+  ((void(*)(void)) _app_start[1])();
   return 0;
 }
 
diff --git a/board/spi_flasher.h b/board/spi_flasher.h
index 94d41c7e326c64..85ad85a39154bd 100644
--- a/board/spi_flasher.h
+++ b/board/spi_flasher.h
@@ -92,8 +92,17 @@ int usb_cb_control_msg(USB_Setup_TypeDef *setup, uint8_t *resp, bool hardwired)
   return resp_len;
 }
 
-int usb_cb_ep1_in(uint8_t *usbdata, int len, bool hardwired) { return 0; }
-void usb_cb_ep3_out(uint8_t *usbdata, int len, bool hardwired) { }
+int usb_cb_ep1_in(uint8_t *usbdata, int len, bool hardwired) {
+  UNUSED(usbdata);
+  UNUSED(len);
+  UNUSED(hardwired);
+  return 0;
+}
+void usb_cb_ep3_out(uint8_t *usbdata, int len, bool hardwired) {
+  UNUSED(usbdata);
+  UNUSED(len);
+  UNUSED(hardwired);
+}
 
 int is_enumerated = 0;
 void usb_cb_enumeration_complete() {
@@ -102,6 +111,7 @@ void usb_cb_enumeration_complete() {
 }
 
 void usb_cb_ep2_out(uint8_t *usbdata, int len, bool hardwired) {
+  UNUSED(hardwired);
   set_led(LED_RED, 0);
   for (int i = 0; i < len/4; i++) {
     // program byte 1
@@ -118,6 +128,7 @@ void usb_cb_ep2_out(uint8_t *usbdata, int len, bool hardwired) {
 
 
 int spi_cb_rx(uint8_t *data, int len, uint8_t *data_out) {
+  UNUSED(len);
   int resp_len = 0;
   switch (data[0]) {
     case 0:
@@ -247,7 +258,7 @@ void CAN1_SCE_IRQHandler() {
 
 #endif
 
-void soft_flasher_start() {
+void soft_flasher_start(void) {
   puts("\n\n\n************************ FLASHER START ************************\n");
 
   enter_bootloader_mode = 0;