diff --git a/include/sway/config.h b/include/sway/config.h
index 1c6e2ac4..5e28c678 100644
--- a/include/sway/config.h
+++ b/include/sway/config.h
@@ -469,7 +469,7 @@ struct seat_config *copy_seat_config(struct seat_config *seat);
 
 void free_seat_config(struct seat_config *ic);
 
-struct seat_attachment_config *seat_attachment_config_new();
+struct seat_attachment_config *seat_attachment_config_new(void);
 
 struct seat_attachment_config *seat_config_get_attachment(
 		struct seat_config *seat_config, char *identifier);
diff --git a/include/sway/debug.h b/include/sway/debug.h
index bf3a5f6d..0e9bb056 100644
--- a/include/sway/debug.h
+++ b/include/sway/debug.h
@@ -17,6 +17,6 @@ struct sway_debug {
 
 extern struct sway_debug debug;
 
-void update_debug_tree();
+void update_debug_tree(void);
 
 #endif
diff --git a/include/sway/ipc-json.h b/include/sway/ipc-json.h
index fef243e3..1cbfd15d 100644
--- a/include/sway/ipc-json.h
+++ b/include/sway/ipc-json.h
@@ -4,7 +4,7 @@
 #include "sway/tree/container.h"
 #include "sway/input/input-manager.h"
 
-json_object *ipc_json_get_version();
+json_object *ipc_json_get_version(void);
 
 json_object *ipc_json_describe_disabled_output(struct sway_output *o);
 json_object *ipc_json_describe_node(struct sway_node *node);
diff --git a/include/swaybar/config.h b/include/swaybar/config.h
index 6739c28a..5f5688cf 100644
--- a/include/swaybar/config.h
+++ b/include/swaybar/config.h
@@ -50,7 +50,7 @@ struct swaybar_config {
 	} colors;
 };
 
-struct swaybar_config *init_config();
+struct swaybar_config *init_config(void);
 void free_config(struct swaybar_config *config);
 uint32_t parse_position(const char *position);
 
diff --git a/sway/config/seat.c b/sway/config/seat.c
index 83dac4c0..46456caf 100644
--- a/sway/config/seat.c
+++ b/sway/config/seat.c
@@ -30,7 +30,7 @@ struct seat_config *new_seat_config(const char* name) {
 	return seat;
 }
 
-struct seat_attachment_config *seat_attachment_config_new() {
+struct seat_attachment_config *seat_attachment_config_new(void) {
 	struct seat_attachment_config *attachment =
 		calloc(1, sizeof(struct seat_attachment_config));
 	if (!attachment) {
diff --git a/sway/debug-tree.c b/sway/debug-tree.c
index 9644f4e5..16b479f9 100644
--- a/sway/debug-tree.c
+++ b/sway/debug-tree.c
@@ -120,7 +120,7 @@ static int draw_node(cairo_t *cairo, struct sway_node *node,
 	return height;
 }
 
-void update_debug_tree() {
+void update_debug_tree(void) {
 	if (!debug.render_tree) {
 		return;
 	}
diff --git a/sway/input/cursor.c b/sway/input/cursor.c
index 2d5d351f..3ddc27a0 100644
--- a/sway/input/cursor.c
+++ b/sway/input/cursor.c
@@ -30,7 +30,7 @@
 // when dragging to the edge of a layout container.
 #define DROP_LAYOUT_BORDER 30
 
-static uint32_t get_current_time_msec() {
+static uint32_t get_current_time_msec(void) {
 	struct timespec now;
 	clock_gettime(CLOCK_MONOTONIC, &now);
 	return now.tv_nsec / 1000;
diff --git a/sway/ipc-json.c b/sway/ipc-json.c
index f054ac9f..45915094 100644
--- a/sway/ipc-json.c
+++ b/sway/ipc-json.c
@@ -42,7 +42,7 @@ static const char *ipc_json_orientation_description(enum sway_container_layout l
 	return "none";
 }
 
-json_object *ipc_json_get_version() {
+json_object *ipc_json_get_version(void) {
 	int major = 0, minor = 0, patch = 0;
 	json_object *version = json_object_new_object();
 
diff --git a/sway/main.c b/sway/main.c
index 80111b8f..50b05b21 100644
--- a/sway/main.c
+++ b/sway/main.c
@@ -41,7 +41,7 @@ void sig_handler(int signal) {
 	sway_terminate(EXIT_SUCCESS);
 }
 
-void detect_raspi() {
+void detect_raspi(void) {
 	bool raspi = false;
 	FILE *f = fopen("/sys/firmware/devicetree/base/model", "r");
 	if (!f) {
@@ -81,7 +81,7 @@ void detect_raspi() {
 	}
 }
 
-void detect_proprietary() {
+void detect_proprietary(void) {
 	FILE *f = fopen("/proc/modules", "r");
 	if (!f) {
 		return;
@@ -116,7 +116,7 @@ void run_as_ipc_client(char *command, char *socket_path) {
 	close(socketfd);
 }
 
-static void log_env() {
+static void log_env(void) {
 	const char *log_vars[] = {
 		"PATH",
 		"LD_LIBRARY_PATH",
@@ -131,7 +131,7 @@ static void log_env() {
 	}
 }
 
-static void log_distro() {
+static void log_distro(void) {
 	const char *paths[] = {
 		"/etc/lsb-release",
 		"/etc/os-release",
@@ -158,7 +158,7 @@ static void log_distro() {
 	}
 }
 
-static void log_kernel() {
+static void log_kernel(void) {
 	FILE *f = popen("uname -a", "r");
 	if (!f) {
 		wlr_log(WLR_INFO, "Unable to determine kernel version");
diff --git a/sway/tree/container.c b/sway/tree/container.c
index baaa82fd..66370a42 100644
--- a/sway/tree/container.c
+++ b/sway/tree/container.c
@@ -593,7 +593,7 @@ void container_update_representation(struct sway_container *con) {
 	}
 }
 
-size_t container_titlebar_height() {
+size_t container_titlebar_height(void) {
 	return config->font_height + TITLEBAR_V_PADDING * 2;
 }
 
diff --git a/swaybar/config.c b/swaybar/config.c
index db7b0db6..4e851cca 100644
--- a/swaybar/config.c
+++ b/swaybar/config.c
@@ -22,7 +22,7 @@ uint32_t parse_position(const char *position) {
 	}
 }
 
-struct swaybar_config *init_config() {
+struct swaybar_config *init_config(void) {
 	struct swaybar_config *config = calloc(1, sizeof(struct swaybar_config));
 	config->status_command = NULL;
 	config->pango_markup = false;
diff --git a/swayidle/main.c b/swayidle/main.c
index 678d622f..5b6c95a7 100644
--- a/swayidle/main.c
+++ b/swayidle/main.c
@@ -92,7 +92,7 @@ static int release_lock(void *data) {
 	return 0;
 }
 
-void acquire_sleep_lock() {
+void acquire_sleep_lock(void) {
 	sd_bus_message *msg = NULL;
 	sd_bus_error error = SD_BUS_ERROR_NULL;
 	struct sd_bus *bus;
@@ -161,7 +161,7 @@ static int dbus_event(int fd, uint32_t mask, void *data) {
 	return 1;
 }
 
-void setup_sleep_listener() {
+void setup_sleep_listener(void) {
 	struct sd_bus *bus;
 
 	int ret = sd_bus_default_system(&bus);
diff --git a/swaylock/main.c b/swaylock/main.c
index 693cbc10..ed8c5607 100644
--- a/swaylock/main.c
+++ b/swaylock/main.c
@@ -32,7 +32,7 @@ void sway_terminate(int exit_code) {
 	exit(exit_code);
 }
 
-static void daemonize() {
+static void daemonize(void) {
 	int fds[2];
 	if (pipe(fds) != 0) {
 		wlr_log(WLR_ERROR, "Failed to pipe");
diff --git a/swaynag/config.c b/swaynag/config.c
index 4d0824c9..cd34dcc2 100644
--- a/swaynag/config.c
+++ b/swaynag/config.c
@@ -11,7 +11,7 @@
 #include "util.h"
 #include "wlr-layer-shell-unstable-v1-client-protocol.h"
 
-static char *read_from_stdin() {
+static char *read_from_stdin(void) {
 	char *buffer = NULL;
 	while (!feof(stdin)) {
 		char *line = read_line(stdin);