diff --git a/firmware/common/fault_handler.c b/firmware/common/fault_handler.c
index 413ce8a8..63c868d8 100644
--- a/firmware/common/fault_handler.c
+++ b/firmware/common/fault_handler.c
@@ -73,17 +73,17 @@ __attribute__((used)) void hard_fault_handler_c(uint32_t* args)
 	while (1) {}
 }
 
-void mem_manage_handler()
+void mem_manage_handler(void)
 {
 	while (1) {}
 }
 
-void bus_fault_handler()
+void bus_fault_handler(void)
 {
 	while (1) {}
 }
 
-void usage_fault_handler()
+void usage_fault_handler(void)
 {
 	while (1) {}
 }
diff --git a/firmware/common/fpga.h b/firmware/common/fpga.h
index fb4270a8..b7bb90bb 100644
--- a/firmware/common/fpga.h
+++ b/firmware/common/fpga.h
@@ -76,8 +76,8 @@ void fpga_set_tx_nco_enable(fpga_driver_t* const drv, const bool enable);
 void fpga_set_tx_nco_pstep(fpga_driver_t* const drv, const uint8_t phase_increment);
 
 bool fpga_image_load(unsigned int index);
-bool fpga_spi_selftest();
-bool fpga_sgpio_selftest();
-bool fpga_if_xcvr_selftest();
+bool fpga_spi_selftest(void);
+bool fpga_sgpio_selftest(void);
+bool fpga_if_xcvr_selftest(void);
 
 #endif // __FPGA_H
diff --git a/firmware/common/fpga_selftest.c b/firmware/common/fpga_selftest.c
index 287c6adc..c5162448 100644
--- a/firmware/common/fpga_selftest.c
+++ b/firmware/common/fpga_selftest.c
@@ -50,7 +50,7 @@ static int rx_samples(const unsigned int num_samples, uint32_t max_cycles)
 	return rc;
 }
 
-bool fpga_spi_selftest()
+bool fpga_spi_selftest(void)
 {
 	// Skip if FPGA configuration failed.
 	if (selftest.fpga_image_load != PASSED) {
@@ -81,7 +81,7 @@ static uint8_t lfsr_advance(uint8_t v)
 	return (v << 1) | feedback;
 }
 
-bool fpga_sgpio_selftest()
+bool fpga_sgpio_selftest(void)
 {
 	bool timeout = false;
 
@@ -168,7 +168,7 @@ static bool in_range(int value, int expected, int error)
 	return (value > min) && (value < max);
 }
 
-bool fpga_if_xcvr_selftest()
+bool fpga_if_xcvr_selftest(void)
 {
 	bool timeout = false;
 
diff --git a/firmware/common/gpdma.c b/firmware/common/gpdma.c
index ac51f432..42ba78b4 100644
--- a/firmware/common/gpdma.c
+++ b/firmware/common/gpdma.c
@@ -24,7 +24,7 @@
 
 #include <libopencm3/lpc43xx/gpdma.h>
 
-void gpdma_controller_enable()
+void gpdma_controller_enable(void)
 {
 	GPDMA_CONFIG |= GPDMA_CONFIG_E(1);
 	while ((GPDMA_CONFIG & GPDMA_CONFIG_E_MASK) == 0) {}
diff --git a/firmware/common/gpdma.h b/firmware/common/gpdma.h
index e14b0c41..053f83a8 100644
--- a/firmware/common/gpdma.h
+++ b/firmware/common/gpdma.h
@@ -28,7 +28,7 @@
 
 #include <libopencm3/lpc43xx/gpdma.h>
 
-void gpdma_controller_enable();
+void gpdma_controller_enable(void);
 
 void gpdma_channel_enable(const uint_fast8_t channel);
 void gpdma_channel_disable(const uint_fast8_t channel);
diff --git a/firmware/common/gpio.h b/firmware/common/gpio.h
index 868fc628..a492e62b 100644
--- a/firmware/common/gpio.h
+++ b/firmware/common/gpio.h
@@ -27,7 +27,7 @@
 
 typedef const struct gpio_t* gpio_t;
 
-void gpio_init();
+void gpio_init(void);
 void gpio_set(gpio_t gpio);
 void gpio_clear(gpio_t gpio);
 void gpio_toggle(gpio_t gpio);
diff --git a/firmware/common/gpio_lpc.c b/firmware/common/gpio_lpc.c
index d05b7fa8..7407cc39 100644
--- a/firmware/common/gpio_lpc.c
+++ b/firmware/common/gpio_lpc.c
@@ -24,7 +24,7 @@
 
 #include <stddef.h>
 
-void gpio_init()
+void gpio_init(void)
 {
 	for (size_t i = 0; i < 8; i++) {
 		GPIO_LPC_PORT(i)->dir = 0;
diff --git a/firmware/common/ice40_spi.c b/firmware/common/ice40_spi.c
index d3ac713c..25a3061f 100644
--- a/firmware/common/ice40_spi.c
+++ b/firmware/common/ice40_spi.c
@@ -54,17 +54,17 @@ void ice40_spi_write(ice40_spi_driver_t* const drv, uint8_t r, uint16_t v)
 	spi_bus_transfer(drv->bus, value, 3);
 }
 
-static void spi_ssp1_wait_for_tx_fifo_not_full()
+static void spi_ssp1_wait_for_tx_fifo_not_full(void)
 {
 	while ((SSP_SR(SSP1_BASE) & SSP_SR_TNF) == 0) {}
 }
 
-static void spi_ssp1_wait_for_rx_fifo_not_empty()
+static void spi_ssp1_wait_for_rx_fifo_not_empty(void)
 {
 	while ((SSP_SR(SSP1_BASE) & SSP_SR_RNE) == 0) {}
 }
 
-static void spi_ssp1_wait_for_not_busy()
+static void spi_ssp1_wait_for_not_busy(void)
 {
 	while (SSP_SR(SSP1_BASE) & SSP_SR_BSY) {}
 }
diff --git a/firmware/common/m0_sleep.c b/firmware/common/m0_sleep.c
index 722c6f10..09067bc6 100644
--- a/firmware/common/m0_sleep.c
+++ b/firmware/common/m0_sleep.c
@@ -20,7 +20,7 @@
  * Boston, MA 02110-1301, USA.
  */
 
-int main()
+int main(void)
 {
 	while (1) {}
 }
diff --git a/firmware/common/operacake_sctimer.c b/firmware/common/operacake_sctimer.c
index fca5d03b..cecfb989 100644
--- a/firmware/common/operacake_sctimer.c
+++ b/firmware/common/operacake_sctimer.c
@@ -55,7 +55,7 @@ static uint32_t default_output = 0;
  * On Praline, instead, MS0/CLK1 (SCT_CLK) is configured to output its
  * clock (f=2 * sample clock) to the SCTimer.
  */
-void operacake_sctimer_init()
+void operacake_sctimer_init(void)
 {
 	// We start by resetting the SCTimer
 	RESET_CTRL1 = RESET_CTRL1_SCT_RST;
@@ -216,7 +216,7 @@ void operacake_sctimer_set_dwell_times(struct operacake_dwell_times* times, int
 	SCT_CTRL &= ~SCT_CTRL_HALT_L(1);
 }
 
-void operacake_sctimer_stop()
+void operacake_sctimer_stop(void)
 {
 	// Halt timer
 	SCT_CTRL |= SCT_CTRL_HALT_L(1);
@@ -228,7 +228,7 @@ void operacake_sctimer_stop()
  * called by set_transceiver_mode so the HackRF starts capturing with the
  * same antenna selected each time.
  */
-void operacake_sctimer_reset_state()
+void operacake_sctimer_reset_state(void)
 {
 	SCT_CTRL |= SCT_CTRL_HALT_L(1);
 
diff --git a/firmware/common/operacake_sctimer.h b/firmware/common/operacake_sctimer.h
index 6c5d0f61..805b3cf9 100644
--- a/firmware/common/operacake_sctimer.h
+++ b/firmware/common/operacake_sctimer.h
@@ -32,10 +32,10 @@ struct operacake_dwell_times {
 	uint8_t port;
 };
 
-void operacake_sctimer_init();
+void operacake_sctimer_init(void);
 void operacake_sctimer_enable(bool enable);
 void operacake_sctimer_set_dwell_times(struct operacake_dwell_times* times, int n);
-void operacake_sctimer_stop();
-void operacake_sctimer_reset_state();
+void operacake_sctimer_stop(void);
+void operacake_sctimer_reset_state(void);
 
 #endif /* __OPERACAKE_SCTIMER_H */
diff --git a/firmware/common/portapack.c b/firmware/common/portapack.c
index e123affa..7b84b432 100644
--- a/firmware/common/portapack.c
+++ b/firmware/common/portapack.c
@@ -70,7 +70,7 @@ static portapack_if_t portapack_if = {
 #define GPIO_DATA_SHIFT (8)
 static const uint32_t gpio_data_mask = 0xFFU << GPIO_DATA_SHIFT;
 
-static void portapack_data_mask_set()
+static void portapack_data_mask_set(void)
 {
 	portapack_if.gpio_port_data->mask = ~gpio_data_mask;
 }
@@ -87,13 +87,13 @@ static void portapack_data_write_high(const uint32_t value)
 	portapack_if.gpio_port_data->mpin = value;
 }
 
-static void portapack_dir_read()
+static void portapack_dir_read(void)
 {
 	portapack_if.gpio_port_data->dir &= ~gpio_data_mask;
 	gpio_set(portapack_if.gpio_dir);
 }
 
-static void portapack_dir_write()
+static void portapack_dir_write(void)
 {
 	gpio_clear(portapack_if.gpio_dir);
 	portapack_if.gpio_port_data->dir |= gpio_data_mask;
@@ -105,32 +105,32 @@ static void portapack_dir_write()
 	 */
 }
 
-__attribute__((unused)) static void portapack_lcd_rd_assert()
+__attribute__((unused)) static void portapack_lcd_rd_assert(void)
 {
 	gpio_clear(portapack_if.gpio_lcd_rdx);
 }
 
-static void portapack_lcd_rd_deassert()
+static void portapack_lcd_rd_deassert(void)
 {
 	gpio_set(portapack_if.gpio_lcd_rdx);
 }
 
-static void portapack_lcd_wr_assert()
+static void portapack_lcd_wr_assert(void)
 {
 	gpio_clear(portapack_if.gpio_lcd_wrx);
 }
 
-static void portapack_lcd_wr_deassert()
+static void portapack_lcd_wr_deassert(void)
 {
 	gpio_set(portapack_if.gpio_lcd_wrx);
 }
 
-static void portapack_io_stb_assert()
+static void portapack_io_stb_assert(void)
 {
 	gpio_clear(portapack_if.gpio_io_stbx);
 }
 
-static void portapack_io_stb_deassert()
+static void portapack_io_stb_deassert(void)
 {
 	gpio_set(portapack_if.gpio_io_stbx);
 }
@@ -188,7 +188,7 @@ static void portapack_io_write(const bool address, const uint_fast16_t value)
 	portapack_io_stb_deassert();
 }
 
-static void portapack_if_init()
+static void portapack_if_init(void)
 {
 	portapack_data_mask_set();
 	portapack_data_write_high(0);
@@ -242,7 +242,7 @@ static void portapack_lcd_data_write_command_and_data(
 	}
 }
 
-static void portapack_lcd_sleep_out()
+static void portapack_lcd_sleep_out(void)
 {
 	const uint8_t cmd_11[] = {};
 	portapack_lcd_data_write_command_and_data(0x11, cmd_11, ARRAY_SIZEOF(cmd_11));
@@ -252,13 +252,13 @@ static void portapack_lcd_sleep_out()
 	portapack_sleep_milliseconds(120);
 }
 
-static void portapack_lcd_display_on()
+static void portapack_lcd_display_on(void)
 {
 	const uint8_t cmd_29[] = {};
 	portapack_lcd_data_write_command_and_data(0x29, cmd_29, ARRAY_SIZEOF(cmd_29));
 }
 
-static void portapack_lcd_ramwr_start()
+static void portapack_lcd_ramwr_start(void)
 {
 	const uint8_t cmd_2c[] = {};
 	portapack_lcd_data_write_command_and_data(0x2c, cmd_2c, ARRAY_SIZEOF(cmd_2c));
@@ -306,13 +306,13 @@ static void portapack_lcd_write_pixels_color(const ui_color_t c, size_t n)
 	}
 }
 
-static void portapack_lcd_wake()
+static void portapack_lcd_wake(void)
 {
 	portapack_lcd_sleep_out();
 	portapack_lcd_display_on();
 }
 
-static void portapack_lcd_reset()
+static void portapack_lcd_reset(void)
 {
 	portapack_lcd_reset_state(false);
 	portapack_sleep_milliseconds(1);
@@ -322,7 +322,7 @@ static void portapack_lcd_reset()
 	portapack_sleep_milliseconds(120);
 }
 
-static void portapack_lcd_init()
+static void portapack_lcd_init(void)
 {
 	// LCDs are configured for IM[2:0] = 001
 	// 8080-I system, 16-bit parallel bus
diff --git a/firmware/common/rad1o/decoder.c b/firmware/common/rad1o/decoder.c
index 46791756..b5450194 100644
--- a/firmware/common/rad1o/decoder.c
+++ b/firmware/common/rad1o/decoder.c
@@ -12,7 +12,7 @@ static const uint8_t* data;
 static uint8_t charBuf[MAXCHR];
 
 // Get next nibble
-static uint8_t gnn()
+static uint8_t gnn(void)
 {
 	static uint8_t byte;
 	uint8_t val;
diff --git a/firmware/common/rad1o/display.c b/firmware/common/rad1o/display.c
index 517db0a0..6e1cf198 100644
--- a/firmware/common/rad1o/display.c
+++ b/firmware/common/rad1o/display.c
@@ -30,7 +30,7 @@ static uint8_t lcdBuffer[RESX * RESY];
 
 static bool isTurned;
 
-static void select()
+static void select(void)
 {
 	/*
      * The LCD requires 9-Bit frames
@@ -58,7 +58,7 @@ static void select()
 	gpio_clear(&gpio_lcd_cs);
 }
 
-static void deselect()
+static void deselect(void)
 {
 	gpio_set(&gpio_lcd_cs);
 }
diff --git a/firmware/common/ui_portapack.c b/firmware/common/ui_portapack.c
index 9918157c..3e8d3013 100644
--- a/firmware/common/ui_portapack.c
+++ b/firmware/common/ui_portapack.c
@@ -489,7 +489,7 @@ static void portapack_radio_path_item_update(
 static rf_path_direction_t portapack_direction = RF_PATH_DIRECTION_OFF;
 static bool portapack_lna_on = false;
 
-static void portapack_radio_path_redraw()
+static void portapack_radio_path_redraw(void)
 {
 	for (size_t i = 0; i < ARRAY_SIZEOF(radio_draw_list); i++) {
 		portapack_draw_radio_path_item(i);
@@ -736,7 +736,7 @@ const hackrf_ui_t portapack_hackrf_ui = {
 	&portapack_ui_operacake_gpio_compatible,
 };
 
-const hackrf_ui_t* portapack_hackrf_ui_init()
+const hackrf_ui_t* portapack_hackrf_ui_init(void)
 {
 	if (portapack()) {
 		return &portapack_hackrf_ui;
diff --git a/firmware/common/ui_portapack.h b/firmware/common/ui_portapack.h
index d712c895..0565cf6a 100644
--- a/firmware/common/ui_portapack.h
+++ b/firmware/common/ui_portapack.h
@@ -25,6 +25,6 @@
 
 #include "hackrf_ui.h"
 
-const hackrf_ui_t* portapack_hackrf_ui_init() __attribute__((weak));
+const hackrf_ui_t* portapack_hackrf_ui_init(void) __attribute__((weak));
 
 #endif /*__UI_PORTAPACK_H__*/
diff --git a/firmware/common/usb.c b/firmware/common/usb.c
index 9188da73..85795ec9 100644
--- a/firmware/common/usb.c
+++ b/firmware/common/usb.c
@@ -67,7 +67,7 @@ static uint_fast8_t usb_endpoint_number(const uint_fast8_t endpoint_address)
 	return (endpoint_address & 0xF);
 }
 
-void usb_peripheral_reset()
+void usb_peripheral_reset(void)
 {
 	RESET_CTRL0 = RESET_CTRL0_USB0_RST;
 	RESET_CTRL0 = 0;
@@ -75,7 +75,7 @@ void usb_peripheral_reset()
 	while ((RESET_ACTIVE_STATUS0 & RESET_CTRL0_USB0_RST) == 0) {}
 }
 
-void usb_phy_enable()
+void usb_phy_enable(void)
 {
 	CREG_CREG0 &= ~CREG_CREG0_USB0PHY;
 }
@@ -634,7 +634,7 @@ static void usb_check_for_transfer_events(void)
 	}
 }
 
-void usb0_isr()
+void usb0_isr(void)
 {
 	const uint32_t status = usb_get_status();
 
diff --git a/firmware/hackrf_usb/hackrf_usb.c b/firmware/hackrf_usb/hackrf_usb.c
index 0b5d303a..5206541a 100644
--- a/firmware/hackrf_usb/hackrf_usb.c
+++ b/firmware/hackrf_usb/hackrf_usb.c
@@ -239,7 +239,7 @@ static bool cpld_jtag_sram_load(jtag_t* const jtag)
 }
 #endif
 
-static void m0_rom_to_ram()
+static void m0_rom_to_ram(void)
 {
 	uint32_t* dest = &__ram_m0_start__;