diff --git a/targets/stm32l432/src/ams.c b/targets/stm32l432/src/ams.c
index 9212d53..5b2b7f7 100644
--- a/targets/stm32l432/src/ams.c
+++ b/targets/stm32l432/src/ams.c
@@ -8,21 +8,25 @@
 #include "device.h"
 #include "nfc.h"
 
-static void flush_rx()
+static void flush_rx(void)
 {
     while(LL_SPI_IsActiveFlag_RXNE(SPI1) != 0)
     {
         LL_SPI_ReceiveData8(SPI1);
     }
 }
-static void wait_for_tx()
+
+
+static void wait_for_tx(void)
 {
     // while (LL_SPI_IsActiveFlag_BSY(SPI1) == 1)
     //     ;
     while(LL_SPI_GetTxFIFOLevel(SPI1) != LL_SPI_TX_FIFO_EMPTY)
         ;
 }
-static void wait_for_rx()
+
+
+static void wait_for_rx(void)
 {
     while(LL_SPI_IsActiveFlag_RXNE(SPI1) == 0)
         ;
@@ -270,7 +274,7 @@ void ams_print_int1(uint8_t int0)
 #endif
 }
 
-int ams_init()
+int ams_init(void)
 {
     LL_GPIO_SetPinMode(SOLO_AMS_CS_PORT,SOLO_AMS_CS_PIN,LL_GPIO_MODE_OUTPUT);
     LL_GPIO_SetOutputPin(SOLO_AMS_CS_PORT,SOLO_AMS_CS_PIN);
@@ -292,7 +296,7 @@ int ams_init()
     return 0;
 }
 
-void ams_configure()
+void ams_configure(void)
 {
     // Should not be used during passive operation.
     uint8_t block[4];
diff --git a/targets/stm32l432/src/ams.h b/targets/stm32l432/src/ams.h
index 8828eaa..e818877 100644
--- a/targets/stm32l432/src/ams.h
+++ b/targets/stm32l432/src/ams.h
@@ -39,8 +39,8 @@ typedef union
 #define SELECT() LL_GPIO_ResetOutputPin(SOLO_AMS_CS_PORT,SOLO_AMS_CS_PIN)
 #define UNSELECT() LL_GPIO_SetOutputPin(SOLO_AMS_CS_PORT,SOLO_AMS_CS_PIN)
 
-int ams_init();
-void ams_configure();
+int ams_init(void);
+void ams_configure(void);
 
 void ams_read_buffer(uint8_t * data, int len);
 void ams_write_buffer(uint8_t * data, int len);
diff --git a/targets/stm32l432/src/crypto.c b/targets/stm32l432/src/crypto.c
index 1dde2f3..69ab4ec 100644
--- a/targets/stm32l432/src/crypto.c
+++ b/targets/stm32l432/src/crypto.c
@@ -61,12 +61,13 @@ static uint8_t master_secret[64];
 static uint8_t transport_secret[32];
 
 
-void crypto_sha256_init()
+void crypto_sha256_init(void)
 {
     sha256_init(&sha256_ctx);
 }
 
-void crypto_sha512_init() {
+void crypto_sha512_init(void)
+{
     cf_sha512_init(&sha512_ctx);
 }
 
@@ -79,7 +80,7 @@ void crypto_load_master_secret(uint8_t * key)
     memmove(transport_secret, key+64, 32);
 }
 
-void crypto_reset_master_secret()
+void crypto_reset_master_secret(void)
 {
     memset(master_secret, 0, 64);
     memset(transport_secret, 0, 32);
@@ -107,7 +108,8 @@ void crypto_sha256_final(uint8_t * hash)
     sha256_final(&sha256_ctx, hash);
 }
 
-void crypto_sha512_final(uint8_t * hash) {
+void crypto_sha512_final(uint8_t * hash)
+{
     // NB: there is also cf_sha512_digest
     cf_sha512_digest_final(&sha512_ctx, hash);
 }
@@ -183,14 +185,14 @@ void crypto_sha256_hmac_final(uint8_t * key, uint32_t klen, uint8_t * hmac)
 }
 
 
-void crypto_ecc256_init()
+void crypto_ecc256_init(void)
 {
     uECC_set_rng((uECC_RNG_Function)ctap_generate_rng);
     _es256_curve = uECC_secp256r1();
 }
 
 
-void crypto_ecc256_load_attestation_key()
+void crypto_ecc256_load_attestation_key(void)
 {
     static uint8_t _key [32];
     memmove(_key, (uint8_t*)ATTESTATION_KEY_ADDR, 32);
diff --git a/targets/stm32l432/src/device.c b/targets/stm32l432/src/device.c
index 532c407..b761801 100644
--- a/targets/stm32l432/src/device.c
+++ b/targets/stm32l432/src/device.c
@@ -34,7 +34,7 @@
 #define LOW_FREQUENCY        1
 #define HIGH_FREQUENCY       0
 
-void wait_for_usb_tether();
+void wait_for_usb_tether(void);
 
 
 uint32_t __90_ms = 0;
@@ -48,12 +48,12 @@ static bool isLowFreq = 0;
 static bool _up_disabled = false;
 
 // #define IS_BUTTON_PRESSED()         (0  == (LL_GPIO_ReadInputPort(SOLO_BUTTON_PORT) & SOLO_BUTTON_PIN))
-static int is_physical_button_pressed()
+static int is_physical_button_pressed(void)
 {
     return (0  == (LL_GPIO_ReadInputPort(SOLO_BUTTON_PORT) & SOLO_BUTTON_PIN));
 }
 
-static int is_touch_button_pressed()
+static int is_touch_button_pressed(void)
 {
     int is_pressed = (tsc_read_button(0) || tsc_read_button(1));
 #ifndef IS_BOOTLOADER
@@ -69,7 +69,7 @@ static int is_touch_button_pressed()
 
 int (*IS_BUTTON_PRESSED)() = is_physical_button_pressed;
 
-static void edge_detect_touch_button()
+static void edge_detect_touch_button(void)
 {
     static uint8_t last_touch = 0;
     uint8_t current_touch = 0;
@@ -92,12 +92,13 @@ static void edge_detect_touch_button()
 
 }
 
-void device_disable_up(bool disable) {
+void device_disable_up(bool disable)
+{
     _up_disabled = disable;
 }
 
 // Timer6 overflow handler.  happens every ~90ms.
-void TIM6_DAC_IRQHandler()
+void TIM6_DAC_IRQHandler(void)
 {
     // timer is only 16 bits, so roll it over here
     TIM6->SR = 0;
@@ -142,7 +143,7 @@ void USB_IRQHandler(void)
   HAL_PCD_IRQHandler(&hpcd);
 }
 
-uint32_t millis()
+uint32_t millis(void)
 {
     return (((uint32_t)TIM6->CNT) + (__90_ms * 90));
 }
@@ -160,7 +161,7 @@ void device_set_status(uint32_t status)
     __device_status = status;
 }
 
-int device_is_button_pressed()
+int device_is_button_pressed(void)
 {
     return IS_BUTTON_PRESSED();
 }
@@ -171,12 +172,13 @@ void delay(uint32_t ms)
     while ((millis() - time) < ms)
         ;
 }
-void device_reboot()
+
+void device_reboot(void)
 {
     NVIC_SystemReset();
 }
 
-void device_init_button()
+void device_init_button(void)
 {
     if (tsc_sensor_exists())
     {
@@ -226,12 +228,12 @@ void device_init(int argc, char *argv[])
 
 }
 
-int device_is_nfc()
+int device_is_nfc(void)
 {
     return _NFC_status;
 }
 
-void wait_for_usb_tether()
+void wait_for_usb_tether(void)
 {
     while (USBD_OK != CDC_Transmit_FS((uint8_t*)"tethered\r\n", 10) )
         ;
@@ -242,7 +244,7 @@ void wait_for_usb_tether()
         ;
 }
 
-void usbhid_init()
+void usbhid_init(void)
 {
     if (!isLowFreq)
     {
@@ -292,12 +294,12 @@ void ctaphid_write_block(uint8_t * data)
 }
 
 
-void usbhid_close()
+void usbhid_close(void)
 {
 
 }
 
-void main_loop_delay()
+void main_loop_delay(void)
 {
 
 }
@@ -307,13 +309,14 @@ static uint32_t winkt1 = 0;
 #ifdef LED_WINK_VALUE
 static uint32_t winkt2 = 0;
 #endif
-void device_wink()
+
+void device_wink(void)
 {
     wink_time = 10;
     winkt1 = 0;
 }
 
-void heartbeat()
+void heartbeat(void)
 {
     static int state = 0;
     static uint32_t val = (LED_MAX_SCALER - LED_MIN_SCALER)/2;
@@ -382,7 +385,7 @@ void authenticator_read_backup_state(AuthenticatorState * a)
 }
 
 // Return 1 yes backup is init'd, else 0
-int authenticator_is_backup_initialized()
+int authenticator_is_backup_initialized(void)
 {
     uint8_t header[16];
     uint32_t * ptr = (uint32_t *)flash_addr(STATE2_PAGE);
@@ -499,7 +502,7 @@ uint32_t ctap_atomic_count(int sel)
 
 
 
-void device_manage()
+void device_manage(void)
 {
 #if NON_BLOCK_PRINTING
     int i = 10;
@@ -525,7 +528,7 @@ void device_manage()
 #endif
 }
 
-static int handle_packets()
+static int handle_packets(void)
 {
     static uint8_t hidmsg[HID_PACKET_SIZE];
     memset(hidmsg,0, sizeof(hidmsg));
@@ -561,6 +564,7 @@ static int wait_for_button_activate(uint32_t wait)
     } while (!IS_BUTTON_PRESSED());
     return 0;
 }
+
 static int wait_for_button_release(uint32_t wait)
 {
     int ret;
@@ -654,7 +658,7 @@ int ctap_user_verification(uint8_t arg)
     return 1;
 }
 
-void ctap_reset_rk()
+void ctap_reset_rk(void)
 {
     int i;
     printf1(TAG_GREEN, "resetting RK \r\n");
@@ -664,7 +668,7 @@ void ctap_reset_rk()
     }
 }
 
-uint32_t ctap_rk_size()
+uint32_t ctap_rk_size(void)
 {
     return RK_NUM_PAGES * (PAGE_SIZE / sizeof(CTAP_residentKey));
 }
@@ -726,7 +730,7 @@ void ctap_overwrite_rk(int index,CTAP_residentKey * rk)
     }
 }
 
-void boot_st_bootloader()
+void boot_st_bootloader(void)
 {
     __disable_irq();
 
@@ -738,7 +742,7 @@ void boot_st_bootloader()
     ;
 }
 
-void boot_solo_bootloader()
+void boot_solo_bootloader(void)
 {
     LL_IWDG_Enable(IWDG);
 
diff --git a/targets/stm32l432/src/flash.c b/targets/stm32l432/src/flash.c
index c37439d..0dec23d 100644
--- a/targets/stm32l432/src/flash.c
+++ b/targets/stm32l432/src/flash.c
@@ -14,12 +14,12 @@
 #include "log.h"
 #include "device.h"
 
-static void flash_lock()
+static void flash_lock(void)
 {
     FLASH->CR |= (1U<<31);
 }
 
-static void flash_unlock()
+static void flash_unlock(void)
 {
     if (FLASH->CR & FLASH_CR_LOCK)
     {
diff --git a/targets/stm32l432/src/init.c b/targets/stm32l432/src/init.c
index bdf42fa..2f90f72 100644
--- a/targets/stm32l432/src/init.c
+++ b/targets/stm32l432/src/init.c
@@ -699,7 +699,7 @@ void SystemClock_Config_LF20(void)
     SET_BIT(RCC->APB1ENR1, RCC_APB1ENR1_PWREN);
 }
 
-void init_usb()
+void init_usb(void)
 {
     // enable USB power
     SET_BIT(PWR->CR2, PWR_CR2_USV);
diff --git a/targets/stm32l432/src/init.h b/targets/stm32l432/src/init.h
index 729e898..6c11633 100644
--- a/targets/stm32l432/src/init.h
+++ b/targets/stm32l432/src/init.h
@@ -22,7 +22,7 @@
 #ifndef _INIT_H_
 #define _INIT_H_
 
-void init_usb();
+void init_usb(void);
 void init_gpio(void);
 void init_debug_uart(void);
 void init_pwm(void);
diff --git a/targets/stm32l432/src/main.c b/targets/stm32l432/src/main.c
index 76b5632..43c9b8d 100644
--- a/targets/stm32l432/src/main.c
+++ b/targets/stm32l432/src/main.c
@@ -57,10 +57,11 @@ void TIM6_DAC_IRQHandler()
     __90_ms += 1;
 }
 
-uint32_t millis()
+uint32_t millis(void)
 {
     return (((uint32_t)TIM6->CNT) + (__90_ms * 90));
 }
+
 void _Error_Handler(char *file, int line)
 {
     while(1)
diff --git a/targets/stm32l432/src/nfc.c b/targets/stm32l432/src/nfc.c
index 9a69880..acec3d3 100644
--- a/targets/stm32l432/src/nfc.c
+++ b/targets/stm32l432/src/nfc.c
@@ -359,7 +359,7 @@ static uint32_t WTX_timer;
 
 bool WTX_process(int read_timeout);
 
-void WTX_clear()
+void WTX_clear(void)
 {
 	WTX_sent = false;
 	WTX_fail = false;
@@ -374,7 +374,7 @@ bool WTX_on(int WTX_time)
 	return true;
 }
 
-bool WTX_off()
+bool WTX_off(void)
 {
 	WTX_timer = 0;
 
@@ -398,7 +398,7 @@ bool WTX_off()
 	return true;
 }
 
-void WTX_timer_exec()
+void WTX_timer_exec(void)
 {
 	// condition: (timer on) or (not expired[300ms])
 	if ((WTX_timer == 0) || WTX_timer + 300 > millis())
@@ -856,7 +856,7 @@ void nfc_process_iblock(uint8_t * buf, int len)
 static uint8_t ibuf[1024];
 static int ibuflen = 0;
 
-void clear_ibuf()
+void clear_ibuf(void)
 {
 	ibuflen = 0;
 	memset(ibuf, 0, sizeof(ibuf));
@@ -969,7 +969,7 @@ void nfc_process_block(uint8_t * buf, unsigned int len)
     }
 }
 
-int nfc_loop()
+int nfc_loop(void)
 {
     uint8_t buf[32];
     AMS_DEVICE ams;
diff --git a/targets/stm32l432/src/nfc.h b/targets/stm32l432/src/nfc.h
index 96f7cab..bdfe9e7 100644
--- a/targets/stm32l432/src/nfc.h
+++ b/targets/stm32l432/src/nfc.h
@@ -6,9 +6,9 @@
 #include "apdu.h"
 
 // Return number of bytes read if any.
-int nfc_loop();
+int nfc_loop(void);
 
-int nfc_init();
+int nfc_init(void);
 
 typedef struct
 {
@@ -61,6 +61,6 @@ typedef enum
 	APP_FIDO,
 } APPLETS;
 
-void WTX_timer_exec();
+void WTX_timer_exec(void);
 
 #endif
diff --git a/targets/stm32l432/src/sense.c b/targets/stm32l432/src/sense.c
index 7e898ae..37a1656 100644
--- a/targets/stm32l432/src/sense.c
+++ b/targets/stm32l432/src/sense.c
@@ -8,7 +8,7 @@
 #define ELECTRODE_0     TSC_GROUP2_IO1
 #define ELECTRODE_1     TSC_GROUP2_IO2
 
-void tsc_init()
+void tsc_init(void)
 {
     LL_GPIO_InitTypeDef GPIO_InitStruct;
     // Enable TSC clock
@@ -74,7 +74,7 @@ void tsc_set_electrode(uint32_t channel_ids)
     TSC->IOCCR = (channel_ids);
 }
 
-void tsc_start_acq()
+void tsc_start_acq(void)
 {
     TSC->CR &= ~(TSC_CR_START);
 
@@ -86,7 +86,7 @@ void tsc_start_acq()
     TSC->CR |= TSC_CR_START;
 }
 
-void tsc_wait_on_acq()
+void tsc_wait_on_acq(void)
 {
     while ( ! (TSC->ISR & TSC_FLAG_EOA) )
         ;
@@ -117,7 +117,7 @@ uint32_t tsc_read_button(uint32_t index)
     return tsc_read(1) < 45;
 }
 
-int tsc_sensor_exists()
+int tsc_sensor_exists(void)
 {
     static uint8_t does = 0;
     if (does) return 1;
diff --git a/targets/stm32l432/src/sense.h b/targets/stm32l432/src/sense.h
index cbf85f3..c8f7434 100644
--- a/targets/stm32l432/src/sense.h
+++ b/targets/stm32l432/src/sense.h
@@ -3,9 +3,9 @@
 
 #include <stdint.h>
 
-void tsc_init();
+void tsc_init(void);
 
-int tsc_sensor_exists();
+int tsc_sensor_exists(void);
 
 // Read button0 or button1
 // Returns 1 if pressed, 0 if not.