diff --git a/src/audio/SDL_wave.c b/src/audio/SDL_wave.c
index 8b8cd34c0b..8d8b533ccb 100644
--- a/src/audio/SDL_wave.c
+++ b/src/audio/SDL_wave.c
@@ -1436,7 +1436,7 @@ static int PCM_Decode(WaveFile *file, Uint8 **audio_buf, Uint32 *audio_len)
     return 0;
 }
 
-static WaveRiffSizeHint WaveGetRiffSizeHint()
+static WaveRiffSizeHint WaveGetRiffSizeHint(void)
 {
     const char *hint = SDL_GetHint(SDL_HINT_WAVE_RIFF_CHUNK_SIZE);
 
@@ -1455,7 +1455,7 @@ static WaveRiffSizeHint WaveGetRiffSizeHint()
     return RiffSizeNoHint;
 }
 
-static WaveTruncationHint WaveGetTruncationHint()
+static WaveTruncationHint WaveGetTruncationHint(void)
 {
     const char *hint = SDL_GetHint(SDL_HINT_WAVE_TRUNCATION);
 
@@ -1474,7 +1474,7 @@ static WaveTruncationHint WaveGetTruncationHint()
     return TruncNoHint;
 }
 
-static WaveFactChunkHint WaveGetFactChunkHint()
+static WaveFactChunkHint WaveGetFactChunkHint(void)
 {
     const char *hint = SDL_GetHint(SDL_HINT_WAVE_FACT_CHUNK);
 
diff --git a/src/audio/pipewire/SDL_pipewire.c b/src/audio/pipewire/SDL_pipewire.c
index adc8804ff5..2387501c7a 100644
--- a/src/audio/pipewire/SDL_pipewire.c
+++ b/src/audio/pipewire/SDL_pipewire.c
@@ -139,13 +139,13 @@ static int pipewire_dlsym(const char *fn, void **addr)
         return -1;                                             \
     }
 
-static int load_pipewire_library()
+static int load_pipewire_library(void)
 {
     pipewire_handle = SDL_LoadObject(pipewire_library);
     return pipewire_handle != NULL ? 0 : -1;
 }
 
-static void unload_pipewire_library()
+static void unload_pipewire_library(void)
 {
     if (pipewire_handle) {
         SDL_UnloadObject(pipewire_handle);
@@ -157,18 +157,18 @@ static void unload_pipewire_library()
 
 #define SDL_PIPEWIRE_SYM(x) PIPEWIRE_##x = x
 
-static int load_pipewire_library()
+static int load_pipewire_library(void)
 {
     return 0;
 }
 
-static void unload_pipewire_library()
+static void unload_pipewire_library(void)
 { /* Nothing to do */
 }
 
 #endif /* SDL_AUDIO_DRIVER_PIPEWIRE_DYNAMIC */
 
-static int load_pipewire_syms()
+static int load_pipewire_syms(void)
 {
     SDL_PIPEWIRE_SYM(pw_get_library_version);
     SDL_PIPEWIRE_SYM(pw_init);
@@ -209,7 +209,7 @@ SDL_FORCE_INLINE SDL_bool pipewire_version_at_least(int major, int minor, int pa
            (pipewire_version_major > major || pipewire_version_minor > minor || pipewire_version_patch >= patch);
 }
 
-static int init_pipewire_library()
+static int init_pipewire_library(void)
 {
     if (!load_pipewire_library()) {
         if (!load_pipewire_syms()) {
@@ -231,7 +231,7 @@ static int init_pipewire_library()
     return -1;
 }
 
-static void deinit_pipewire_library()
+static void deinit_pipewire_library(void)
 {
     PIPEWIRE_pw_deinit();
     unload_pipewire_library();
@@ -337,7 +337,7 @@ static void io_list_remove(Uint32 id)
     }
 }
 
-static void io_list_sort()
+static void io_list_sort(void)
 {
     struct io_node *default_sink = NULL, *default_source = NULL;
     struct io_node *n, *temp;
@@ -362,7 +362,7 @@ static void io_list_sort()
     }
 }
 
-static void io_list_clear()
+static void io_list_clear(void)
 {
     struct io_node *n, *temp;
 
@@ -423,7 +423,7 @@ static void pending_list_remove(Uint32 id)
     }
 }
 
-static void pending_list_clear()
+static void pending_list_clear(void)
 {
     struct node_object *node, *temp;
 
@@ -748,7 +748,7 @@ static const struct pw_registry_events registry_events = { PW_VERSION_REGISTRY_E
                                                            .global_remove = registry_event_remove_callback };
 
 /* The hotplug thread */
-static int hotplug_loop_init()
+static int hotplug_loop_init(void)
 {
     int res;
 
@@ -791,7 +791,7 @@ static int hotplug_loop_init()
     return 0;
 }
 
-static void hotplug_loop_destroy()
+static void hotplug_loop_destroy(void)
 {
     if (hotplug_loop) {
         PIPEWIRE_pw_thread_loop_stop(hotplug_loop);
@@ -833,7 +833,7 @@ static void hotplug_loop_destroy()
     }
 }
 
-static void PIPEWIRE_DetectDevices()
+static void PIPEWIRE_DetectDevices(void)
 {
     struct io_node *io;
 
@@ -1333,7 +1333,7 @@ failed:
     return ret;
 }
 
-static void PIPEWIRE_Deinitialize()
+static void PIPEWIRE_Deinitialize(void)
 {
     if (pipewire_initialized) {
         hotplug_loop_destroy();
diff --git a/src/audio/pulseaudio/SDL_pulseaudio.c b/src/audio/pulseaudio/SDL_pulseaudio.c
index 93944525f9..8c218ba763 100644
--- a/src/audio/pulseaudio/SDL_pulseaudio.c
+++ b/src/audio/pulseaudio/SDL_pulseaudio.c
@@ -802,7 +802,7 @@ static int SDLCALL HotplugThread(void *data)
     return 0;
 }
 
-static void PULSEAUDIO_DetectDevices()
+static void PULSEAUDIO_DetectDevices(void)
 {
     WaitForPulseOperation(hotplug_mainloop, PULSEAUDIO_pa_context_get_server_info(hotplug_context, ServerInfoCallback, NULL));
     WaitForPulseOperation(hotplug_mainloop, PULSEAUDIO_pa_context_get_sink_info_list(hotplug_context, SinkInfoCallback, (void *)((intptr_t)SDL_TRUE)));
diff --git a/src/core/linux/SDL_evdev_kbd.c b/src/core/linux/SDL_evdev_kbd.c
index e6e4fb3b35..026609b460 100644
--- a/src/core/linux/SDL_evdev_kbd.c
+++ b/src/core/linux/SDL_evdev_kbd.c
@@ -181,8 +181,8 @@ static void SDL_EVDEV_kbd_reraise_signal(int sig)
     (void)raise(sig);
 }
 
-siginfo_t *SDL_EVDEV_kdb_cleanup_siginfo = NULL;
-void *SDL_EVDEV_kdb_cleanup_ucontext = NULL;
+static siginfo_t *SDL_EVDEV_kdb_cleanup_siginfo = NULL;
+static void *SDL_EVDEV_kdb_cleanup_ucontext = NULL;
 
 static void kbd_cleanup_signal_action(int signum, siginfo_t *info, void *ucontext)
 {
@@ -208,7 +208,7 @@ static void kbd_cleanup_signal_action(int signum, siginfo_t *info, void *ucontex
     SDL_EVDEV_kbd_reraise_signal(signum);
 }
 
-static void kbd_unregister_emerg_cleanup()
+static void kbd_unregister_emerg_cleanup(void)
 {
     int tabidx;
 
diff --git a/src/core/linux/SDL_fcitx.c b/src/core/linux/SDL_fcitx.c
index 103d55cc58..7ce6f02285 100644
--- a/src/core/linux/SDL_fcitx.c
+++ b/src/core/linux/SDL_fcitx.c
@@ -53,7 +53,7 @@ typedef struct FcitxClient
 
 static FcitxClient fcitx_client;
 
-static char *GetAppName()
+static char *GetAppName(void)
 {
 #if defined(__LINUX__) || defined(__FREEBSD__)
     char *spot;
@@ -367,7 +367,7 @@ static Uint32 Fcitx_ModState(void)
 }
 
 SDL_bool
-SDL_Fcitx_Init()
+SDL_Fcitx_Init(void)
 {
     fcitx_client.dbus = SDL_DBus_GetContext();
 
@@ -379,7 +379,7 @@ SDL_Fcitx_Init()
     return FcitxClientCreateIC(&fcitx_client);
 }
 
-void SDL_Fcitx_Quit()
+void SDL_Fcitx_Quit(void)
 {
     FcitxClientICCallMethod(&fcitx_client, "DestroyIC");
     if (fcitx_client.ic_path) {
diff --git a/src/core/linux/SDL_ime.c b/src/core/linux/SDL_ime.c
index 36cdbc5263..873709b05b 100644
--- a/src/core/linux/SDL_ime.c
+++ b/src/core/linux/SDL_ime.c
@@ -40,7 +40,7 @@ static SDL_IME_ProcessKeyEvent_t SDL_IME_ProcessKeyEvent_Real = NULL;
 static SDL_IME_UpdateTextRect_t SDL_IME_UpdateTextRect_Real = NULL;
 static SDL_IME_PumpEvents_t SDL_IME_PumpEvents_Real = NULL;
 
-static void InitIME()
+static void InitIME(void)
 {
     static SDL_bool inited = SDL_FALSE;
 #ifdef HAVE_FCITX
@@ -144,7 +144,7 @@ void SDL_IME_UpdateTextRect(const SDL_Rect *rect)
     }
 }
 
-void SDL_IME_PumpEvents()
+void SDL_IME_PumpEvents(void)
 {
     if (SDL_IME_PumpEvents_Real) {
         SDL_IME_PumpEvents_Real();
diff --git a/src/core/linux/SDL_threadprio.c b/src/core/linux/SDL_threadprio.c
index 4543d8da8c..cc690853de 100644
--- a/src/core/linux/SDL_threadprio.c
+++ b/src/core/linux/SDL_threadprio.c
@@ -74,7 +74,7 @@ static SDL_bool realtime_portal_supported(DBusConnection *conn)
                                               "RTTimeUSecMax", DBUS_TYPE_INT64, &res);
 }
 
-static void set_rtkit_interface()
+static void set_rtkit_interface(void)
 {
     SDL_DBusContext *dbus = SDL_DBus_GetContext();
 
@@ -92,7 +92,7 @@ static void set_rtkit_interface()
     }
 }
 
-static DBusConnection *get_rtkit_dbus_connection()
+static DBusConnection *get_rtkit_dbus_connection(void)
 {
     SDL_DBusContext *dbus = SDL_DBus_GetContext();
 
@@ -103,7 +103,7 @@ static DBusConnection *get_rtkit_dbus_connection()
     return NULL;
 }
 
-static void rtkit_initialize()
+static void rtkit_initialize(void)
 {
     DBusConnection *dbus_conn;
 
@@ -129,7 +129,7 @@ static void rtkit_initialize()
     }
 }
 
-static SDL_bool rtkit_initialize_realtime_thread()
+static SDL_bool rtkit_initialize_realtime_thread(void)
 {
     // Following is an excerpt from rtkit README that outlines the requirements
     // a thread must meet before making rtkit requests:
diff --git a/src/events/SDL_events.c b/src/events/SDL_events.c
index 87152d0e64..669c0801c4 100644
--- a/src/events/SDL_events.c
+++ b/src/events/SDL_events.c
@@ -665,7 +665,7 @@ static void SDL_CutEvent(SDL_EventEntry *entry)
     SDL_AtomicAdd(&SDL_EventQ.count, -1);
 }
 
-static int SDL_SendWakeupEvent()
+static int SDL_SendWakeupEvent(void)
 {
     SDL_VideoDevice *_this = SDL_GetVideoDevice();
     if (_this == NULL || !_this->SendWakeupEvent) {
@@ -875,7 +875,7 @@ static void SDL_PumpEventsInternal(SDL_bool push_sentinel)
     }
 }
 
-void SDL_PumpEvents()
+void SDL_PumpEvents(void)
 {
     SDL_PumpEventsInternal(SDL_FALSE);
 }
@@ -887,7 +887,7 @@ int SDL_PollEvent(SDL_Event *event)
     return SDL_WaitEventTimeoutNS(event, 0);
 }
 
-static SDL_bool SDL_events_need_periodic_poll()
+static SDL_bool SDL_events_need_periodic_poll(void)
 {
     SDL_bool need_periodic_poll = SDL_FALSE;
 
@@ -970,7 +970,7 @@ static int SDL_WaitEventTimeout_Device(_THIS, SDL_Window *wakeup_window, SDL_Eve
     return 0;
 }
 
-static SDL_bool SDL_events_need_polling()
+static SDL_bool SDL_events_need_polling(void)
 {
     SDL_bool need_polling = SDL_FALSE;
 
diff --git a/src/events/SDL_keysym_to_scancode.c b/src/events/SDL_keysym_to_scancode.c
index 3379d664de..fbd9fc72f5 100644
--- a/src/events/SDL_keysym_to_scancode.c
+++ b/src/events/SDL_keysym_to_scancode.c
@@ -24,6 +24,7 @@
 
 #include "SDL_keyboard_c.h"
 #include "SDL_scancode_tables_c.h"
+#include "SDL_keysym_to_scancode_c.h"
 
 /* *INDENT-OFF* */ /* clang-format off */
 static const struct {
diff --git a/src/events/SDL_mouse.c b/src/events/SDL_mouse.c
index 869b8672e9..4ff9b87580 100644
--- a/src/events/SDL_mouse.c
+++ b/src/events/SDL_mouse.c
@@ -1073,7 +1073,7 @@ int SDL_SetRelativeMouseMode(SDL_bool enabled)
 }
 
 SDL_bool
-SDL_GetRelativeMouseMode()
+SDL_GetRelativeMouseMode(void)
 {
     SDL_Mouse *mouse = SDL_GetMouse();
 
diff --git a/src/joystick/SDL_gamepad.c b/src/joystick/SDL_gamepad.c
index 12cc397beb..a732e880b7 100644
--- a/src/joystick/SDL_gamepad.c
+++ b/src/joystick/SDL_gamepad.c
@@ -1804,7 +1804,7 @@ char *SDL_GetGamepadMapping(SDL_Gamepad *gamepad)
     return retval;
 }
 
-static void SDL_LoadGamepadHints()
+static void SDL_LoadGamepadHints(void)
 {
     const char *hint = SDL_GetHint(SDL_HINT_GAMECONTROLLERCONFIG);
     if (hint && hint[0]) {
diff --git a/src/joystick/SDL_joystick.c b/src/joystick/SDL_joystick.c
index 63a8842bb5..0013a474ad 100644
--- a/src/joystick/SDL_joystick.c
+++ b/src/joystick/SDL_joystick.c
@@ -196,7 +196,7 @@ static SDL_bool SDL_GetDriverAndJoystickIndex(SDL_JoystickID instance_id, SDL_Jo
     return SDL_FALSE;
 }
 
-static int SDL_FindFreePlayerIndex()
+static int SDL_FindFreePlayerIndex(void)
 {
     int player_index;
 
@@ -395,7 +395,7 @@ SDL_JoystickID *SDL_GetJoysticks(int *count)
  * Return the next available joystick instance ID
  * This may be called by drivers from multiple threads, unprotected by any locks
  */
-SDL_JoystickID SDL_GetNextJoystickInstanceID()
+SDL_JoystickID SDL_GetNextJoystickInstanceID(void)
 {
     return SDL_AtomicIncRef(&SDL_last_joystick_instance_id) + 1;
 }
@@ -1319,7 +1319,7 @@ void SDL_QuitJoysticks(void)
     SDL_UnlockJoysticks();
 }
 
-static SDL_bool SDL_PrivateJoystickShouldIgnoreEvent()
+static SDL_bool SDL_PrivateJoystickShouldIgnoreEvent(void)
 {
     if (SDL_joystick_allows_background_events) {
         return SDL_FALSE;
@@ -1726,7 +1726,7 @@ void SDL_SetJoystickEventsEnabled(SDL_bool enabled)
 #endif /* SDL_EVENTS_DISABLED */
 }
 
-SDL_bool SDL_JoystickEventsEnabled()
+SDL_bool SDL_JoystickEventsEnabled(void)
 {
     SDL_bool enabled = SDL_FALSE;
 
diff --git a/src/render/opengles2/SDL_shaders_gles2.c b/src/render/opengles2/SDL_shaders_gles2.c
index c71356295c..6055bf7723 100644
--- a/src/render/opengles2/SDL_shaders_gles2.c
+++ b/src/render/opengles2/SDL_shaders_gles2.c
@@ -377,7 +377,7 @@ const char *GLES2_GetShaderInclude(GLES2_ShaderIncludeType type)
     }
 }
 
-GLES2_ShaderIncludeType GLES2_GetTexCoordPrecisionEnumFromHint()
+GLES2_ShaderIncludeType GLES2_GetTexCoordPrecisionEnumFromHint(void)
 {
     const char *texcoord_hint = SDL_GetHint("SDL_RENDER_OPENGLES2_TEXCOORD_PRECISION");
     GLES2_ShaderIncludeType value = GLES2_SHADER_FRAGMENT_INCLUDE_BEST_TEXCOORD_PRECISION;
diff --git a/src/sensor/SDL_sensor.c b/src/sensor/SDL_sensor.c
index d974b39c27..31391b40ee 100644
--- a/src/sensor/SDL_sensor.c
+++ b/src/sensor/SDL_sensor.c
@@ -149,7 +149,7 @@ SDL_SensorID *SDL_GetSensors(int *count)
  * Return the next available sensor instance ID
  * This may be called by drivers from multiple threads, unprotected by any locks
  */
-SDL_SensorID SDL_GetNextSensorInstanceID()
+SDL_SensorID SDL_GetNextSensorInstanceID(void)
 {
     return SDL_AtomicIncRef(&SDL_last_sensor_instance_id) + 1;
 }
diff --git a/src/test/SDL_test_assert.c b/src/test/SDL_test_assert.c
index a62816950c..bfe6955c4b 100644
--- a/src/test/SDL_test_assert.c
+++ b/src/test/SDL_test_assert.c
@@ -104,7 +104,7 @@ void SDLTest_AssertPass(SDL_PRINTF_FORMAT_STRING const char *assertDescription,
 /*
  * Resets the assert summary counters to zero.
  */
-void SDLTest_ResetAssertSummary()
+void SDLTest_ResetAssertSummary(void)
 {
     SDLTest_AssertsPassed = 0;
     SDLTest_AssertsFailed = 0;
@@ -114,7 +114,7 @@ void SDLTest_ResetAssertSummary()
  * Logs summary of all assertions (total, pass, fail) since last reset
  * as INFO (failed==0) or ERROR (failed > 0).
  */
-void SDLTest_LogAssertSummary()
+void SDLTest_LogAssertSummary(void)
 {
     int totalAsserts = SDLTest_AssertsPassed + SDLTest_AssertsFailed;
     if (SDLTest_AssertsFailed == 0) {
@@ -127,7 +127,7 @@ void SDLTest_LogAssertSummary()
 /*
  * Converts the current assert state into a test result
  */
-int SDLTest_AssertSummaryToTestResult()
+int SDLTest_AssertSummaryToTestResult(void)
 {
     if (SDLTest_AssertsFailed > 0) {
         return TEST_RESULT_FAILED;
diff --git a/src/thread/SDL_thread.c b/src/thread/SDL_thread.c
index 2381b5acd2..7dbc1bcb0c 100644
--- a/src/thread/SDL_thread.c
+++ b/src/thread/SDL_thread.c
@@ -27,7 +27,7 @@
 #include "../SDL_error_c.h"
 
 SDL_TLSID
-SDL_TLSCreate()
+SDL_TLSCreate(void)
 {
     static SDL_atomic_t SDL_tls_id;
     return SDL_AtomicIncRef(&SDL_tls_id) + 1;
@@ -78,7 +78,7 @@ int SDL_TLSSet(SDL_TLSID id, const void *value, void(SDLCALL *destructor)(void *
     return 0;
 }
 
-void SDL_TLSCleanup()
+void SDL_TLSCleanup(void)
 {
     SDL_TLSData *storage;
 
@@ -194,7 +194,7 @@ int SDL_Generic_SetTLSData(SDL_TLSData *data)
 }
 
 /* Non-thread-safe global error variable */
-static SDL_error *SDL_GetStaticErrBuf()
+static SDL_error *SDL_GetStaticErrBuf(void)
 {
     static SDL_error SDL_global_error;
     static char SDL_global_error_str[128];
diff --git a/src/video/SDL_blit.c b/src/video/SDL_blit.c
index 9d0466ecb1..c9540dac78 100644
--- a/src/video/SDL_blit.c
+++ b/src/video/SDL_blit.c
@@ -102,7 +102,7 @@ static int SDLCALL SDL_SoftBlit(SDL_Surface *src, SDL_Rect *srcrect,
 #ifdef __MACOS__
 #include <sys/sysctl.h>
 
-static SDL_bool SDL_UseAltivecPrefetch()
+static SDL_bool SDL_UseAltivecPrefetch(void)
 {
     const char key[] = "hw.l3cachesize";
     u_int64_t result = 0;
@@ -115,7 +115,7 @@ static SDL_bool SDL_UseAltivecPrefetch()
     }
 }
 #else
-static SDL_bool SDL_UseAltivecPrefetch()
+static SDL_bool SDL_UseAltivecPrefetch(void)
 {
     /* Just guess G4 */
     return SDL_TRUE;
diff --git a/src/video/SDL_stretch.c b/src/video/SDL_stretch.c
index 65bc140d16..05cf102622 100644
--- a/src/video/SDL_stretch.c
+++ b/src/video/SDL_stretch.c
@@ -362,7 +362,7 @@ static void printf_128(const char *str, __m128i var)
 }
 #endif
 
-static SDL_INLINE int hasSSE2()
+static SDL_INLINE int hasSSE2(void)
 {
     static int val = -1;
     if (val != -1) {
@@ -531,7 +531,7 @@ static int scale_mat_SSE(const Uint32 *src, int src_w, int src_h, int src_pitch,
 
 #if defined(HAVE_NEON_INTRINSICS)
 
-static SDL_INLINE int hasNEON()
+static SDL_INLINE int hasNEON(void)
 {
     static int val = -1;
     if (val != -1) {
diff --git a/src/video/SDL_video.c b/src/video/SDL_video.c
index 742b4fc2c7..9a9950d8f0 100644
--- a/src/video/SDL_video.c
+++ b/src/video/SDL_video.c
@@ -3285,7 +3285,7 @@ void SDL_DestroyWindow(SDL_Window *window)
     SDL_free(window);
 }
 
-SDL_bool SDL_ScreenSaverEnabled()
+SDL_bool SDL_ScreenSaverEnabled(void)
 {
     if (_this == NULL) {
         return SDL_TRUE;
@@ -3293,7 +3293,7 @@ SDL_bool SDL_ScreenSaverEnabled()
     return _this->suspend_screensaver ? SDL_FALSE : SDL_TRUE;
 }
 
-int SDL_EnableScreenSaver()
+int SDL_EnableScreenSaver(void)
 {
     if (_this == NULL) {
         return 0;
@@ -3309,7 +3309,7 @@ int SDL_EnableScreenSaver()
     return SDL_Unsupported();
 }
 
-int SDL_DisableScreenSaver()
+int SDL_DisableScreenSaver(void)
 {
     if (_this == NULL) {
         return 0;
@@ -3594,7 +3594,7 @@ void SDL_EGL_SetEGLAttributeCallbacks(SDL_EGLAttribArrayCallback platformAttribC
     _this->egl_contextattrib_callback = contextAttribCallback;
 }
 
-void SDL_GL_ResetAttributes()
+void SDL_GL_ResetAttributes(void)
 {
     if (_this == NULL) {
         return;
diff --git a/src/video/SDL_yuv.c b/src/video/SDL_yuv.c
index 0a603aba43..2df6f64e43 100644
--- a/src/video/SDL_yuv.c
+++ b/src/video/SDL_yuv.c
@@ -38,7 +38,7 @@ void SDL_SetYUVConversionMode(SDL_YUV_CONVERSION_MODE mode)
     SDL_YUV_ConversionMode = mode;
 }
 
-SDL_YUV_CONVERSION_MODE SDL_GetYUVConversionMode()
+SDL_YUV_CONVERSION_MODE SDL_GetYUVConversionMode(void)
 {
     return SDL_YUV_ConversionMode;
 }
diff --git a/src/video/dummy/SDL_nullvideo.c b/src/video/dummy/SDL_nullvideo.c
index f936c8d29e..d1643d119a 100644
--- a/src/video/dummy/SDL_nullvideo.c
+++ b/src/video/dummy/SDL_nullvideo.c
@@ -128,7 +128,7 @@ VideoBootStrap DUMMY_evdev_bootstrap = {
     DUMMY_CreateDevice
 };
 void SDL_EVDEV_Init(void);
-void SDL_EVDEV_Poll();
+void SDL_EVDEV_Poll(void);
 void SDL_EVDEV_Quit(void);
 static void DUMMY_EVDEV_Poll(_THIS)
 {
diff --git a/src/video/wayland/SDL_waylandevents.c b/src/video/wayland/SDL_waylandevents.c
index 56ae6ca34e..1d05b2cd45 100644
--- a/src/video/wayland/SDL_waylandevents.c
+++ b/src/video/wayland/SDL_waylandevents.c
@@ -179,7 +179,7 @@ static struct wl_surface *touch_surface(SDL_TouchID id)
     return NULL;
 }
 
-Uint64 Wayland_GetEventTimestamp(Uint64 nsTimestamp)
+static Uint64 Wayland_GetEventTimestamp(Uint64 nsTimestamp)
 {
     static Uint64 last;
     static Uint64 timestamp_offset;
@@ -2328,7 +2328,7 @@ static void tablet_tool_handle_proximity_out(void *data, struct zwp_tablet_tool_
     }
 }
 
-uint32_t tablet_tool_btn_to_sdl_button(struct SDL_WaylandTabletInput *input)
+static uint32_t tablet_tool_btn_to_sdl_button(struct SDL_WaylandTabletInput *input)
 {
     unsigned int tool_btn = input->btn_stylus3 << 2 | input->btn_stylus2 << 1 | input->btn_stylus << 0;
     switch (tool_btn) {
@@ -2477,7 +2477,7 @@ static const struct zwp_tablet_tool_v2_listener tablet_tool_listener = {
     tablet_tool_handle_frame
 };
 
-struct SDL_WaylandTabletObjectListNode *tablet_object_list_new_node(void *object)
+static struct SDL_WaylandTabletObjectListNode *tablet_object_list_new_node(void *object)
 {
     struct SDL_WaylandTabletObjectListNode *node;
 
@@ -2492,7 +2492,7 @@ struct SDL_WaylandTabletObjectListNode *tablet_object_list_new_node(void *object
     return node;
 }
 
-void tablet_object_list_append(struct SDL_WaylandTabletObjectListNode *head, void *object)
+static void tablet_object_list_append(struct SDL_WaylandTabletObjectListNode *head, void *object)
 {
     if (head->object == NULL) {
         head->object = object;
@@ -2506,7 +2506,7 @@ void tablet_object_list_append(struct SDL_WaylandTabletObjectListNode *head, voi
     head->next = tablet_object_list_new_node(object);
 }
 
-void tablet_object_list_destroy(struct SDL_WaylandTabletObjectListNode *head, void (*deleter)(void *object))
+static void tablet_object_list_destroy(struct SDL_WaylandTabletObjectListNode *head, void (*deleter)(void *object))
 {
     while (head) {
         struct SDL_WaylandTabletObjectListNode *next = head->next;
diff --git a/src/video/wayland/SDL_waylandmouse.c b/src/video/wayland/SDL_waylandmouse.c
index da36b25633..ac9cd257e7 100644
--- a/src/video/wayland/SDL_waylandmouse.c
+++ b/src/video/wayland/SDL_waylandmouse.c
@@ -448,7 +448,7 @@ static SDL_Cursor *Wayland_CreateSystemCursor(SDL_SystemCursor id)
     return cursor;
 }
 
-static SDL_Cursor *Wayland_CreateDefaultCursor()
+static SDL_Cursor *Wayland_CreateDefaultCursor(void)
 {
     return Wayland_CreateSystemCursor(SDL_SYSTEM_CURSOR_ARROW);
 }
diff --git a/src/video/wayland/SDL_waylandsym.h b/src/video/wayland/SDL_waylandsym.h
index 481eeab27b..f2836667bc 100644
--- a/src/video/wayland/SDL_waylandsym.h
+++ b/src/video/wayland/SDL_waylandsym.h
@@ -92,7 +92,7 @@ SDL_WAYLAND_SYM(struct wl_proxy*, wl_proxy_marshal_array_flags, (struct wl_proxy
 
 #if 0 /* TODO RECONNECT: See waylandvideo.c for more information! */
 #if SDL_WAYLAND_CHECK_VERSION(broken, on, purpose)
-SDL_WAYLAND_SYM(int, wl_display_reconnect, (struct wl_display*));
+SDL_WAYLAND_SYM(int, wl_display_reconnect, (struct wl_display*))
 #endif
 #endif /* 0 */
 
@@ -130,7 +130,7 @@ SDL_WAYLAND_SYM(int, xkb_state_key_get_syms, (struct xkb_state *, xkb_keycode_t,
 SDL_WAYLAND_SYM(int, xkb_keysym_to_utf8, (xkb_keysym_t, char *, size_t) )
 SDL_WAYLAND_SYM(struct xkb_keymap *, xkb_keymap_new_from_string, (struct xkb_context *, const char *, enum xkb_keymap_format, enum xkb_keymap_compile_flags))
 SDL_WAYLAND_SYM(struct xkb_state *, xkb_state_new, (struct xkb_keymap *) )
-SDL_WAYLAND_SYM(int, xkb_keymap_key_repeats, (struct xkb_keymap *keymap, xkb_keycode_t key) );
+SDL_WAYLAND_SYM(int, xkb_keymap_key_repeats, (struct xkb_keymap *keymap, xkb_keycode_t key) )
 SDL_WAYLAND_SYM(void, xkb_keymap_unref, (struct xkb_keymap *) )
 SDL_WAYLAND_SYM(void, xkb_state_unref, (struct xkb_state *) )
 SDL_WAYLAND_SYM(void, xkb_context_unref, (struct xkb_context *) )
diff --git a/src/video/wayland/SDL_waylandvideo.c b/src/video/wayland/SDL_waylandvideo.c
index d706303053..9a5c7b9ea8 100644
--- a/src/video/wayland/SDL_waylandvideo.c
+++ b/src/video/wayland/SDL_waylandvideo.c
@@ -71,7 +71,7 @@ static void Wayland_VideoQuit(_THIS);
 
 /* Find out what class name we should use
  * Based on src/video/x11/SDL_x11video.c */
-static char *get_classname()
+static char *get_classname(void)
 {
     /* !!! FIXME: this is probably wrong, albeit harmless in many common cases. From protocol spec:
         "The surface class identifies the general class of applications
diff --git a/src/video/wayland/SDL_waylandwindow.c b/src/video/wayland/SDL_waylandwindow.c
index c84206baf0..6bad7cdadd 100644
--- a/src/video/wayland/SDL_waylandwindow.c
+++ b/src/video/wayland/SDL_waylandwindow.c
@@ -1474,7 +1474,7 @@ int Wayland_FlashWindow(_THIS, SDL_Window *window, SDL_FlashOperation operation)
     return 0;
 }
 
-void handle_preferred_scale_changed(void *data,
+static void handle_preferred_scale_changed(void *data,
                                     struct wp_fractional_scale_v1 *wp_fractional_scale_v1,
                                     uint preferred_scale)
 {
diff --git a/src/video/x11/SDL_x11mouse.c b/src/video/x11/SDL_x11mouse.c
index 3f67950bb3..b8ba1c2559 100644
--- a/src/video/x11/SDL_x11mouse.c
+++ b/src/video/x11/SDL_x11mouse.c
@@ -36,7 +36,7 @@ static Display *GetDisplay(void)
     return SDL_GetVideoDevice()->driverdata->display;
 }
 
-static Cursor X11_CreateEmptyCursor()
+static Cursor X11_CreateEmptyCursor(void)
 {
     if (x11_empty_cursor == None) {
         Display *display = GetDisplay();
@@ -65,7 +65,7 @@ static void X11_DestroyEmptyCursor(void)
     }
 }
 
-static SDL_Cursor *X11_CreateDefaultCursor()
+static SDL_Cursor *X11_CreateDefaultCursor(void)
 {
     SDL_Cursor *cursor;
 
diff --git a/src/video/x11/SDL_x11sym.h b/src/video/x11/SDL_x11sym.h
index d160eae034..17734ad59e 100644
--- a/src/video/x11/SDL_x11sym.h
+++ b/src/video/x11/SDL_x11sym.h
@@ -278,7 +278,7 @@ SDL_X11_SYM(Bool,XIWarpPointer,(Display *a,int b,Window c,Window d,double e,doub
 #if SDL_VIDEO_DRIVER_X11_XRANDR
 SDL_X11_MODULE(XRANDR)
 SDL_X11_SYM(Status,XRRQueryVersion,(Display *dpy,int *major_versionp,int *minor_versionp),(dpy,major_versionp,minor_versionp),return)
-SDL_X11_SYM(Bool,XRRQueryExtension,(Display *dpy,int *event_base_return,int *error_base_return),(dpy,event_base_return,error_base_return),return);
+SDL_X11_SYM(Bool,XRRQueryExtension,(Display *dpy,int *event_base_return,int *error_base_return),(dpy,event_base_return,error_base_return),return)
 SDL_X11_SYM(XRRScreenConfiguration *,XRRGetScreenInfo,(Display *dpy,Drawable draw),(dpy,draw),return)
 SDL_X11_SYM(SizeID,XRRConfigCurrentConfiguration,(XRRScreenConfiguration *config,Rotation *rotation),(config,rotation),return)
 SDL_X11_SYM(short,XRRConfigCurrentRate,(XRRScreenConfiguration *config),(config),return)
diff --git a/src/video/x11/SDL_x11video.c b/src/video/x11/SDL_x11video.c
index d2517772c6..e43ad2388d 100644
--- a/src/video/x11/SDL_x11video.c
+++ b/src/video/x11/SDL_x11video.c
@@ -45,7 +45,7 @@ static int X11_VideoInit(_THIS);
 static void X11_VideoQuit(_THIS);
 
 /* Find out what class name we should use */
-static char *get_classname()
+static char *get_classname(void)
 {
     char *spot;
 #if defined(__LINUX__) || defined(__FREEBSD__)
diff --git a/src/video/x11/SDL_x11xfixes.c b/src/video/x11/SDL_x11xfixes.c
index 7e1748aca3..bd4d2cdeb2 100644
--- a/src/video/x11/SDL_x11xfixes.c
+++ b/src/video/x11/SDL_x11xfixes.c
@@ -64,7 +64,7 @@ void X11_InitXfixes(_THIS)
     xfixes_initialized = 1;
 }
 
-int X11_XfixesIsInitialized()
+int X11_XfixesIsInitialized(void)
 {
     return xfixes_initialized;
 }
diff --git a/src/video/x11/SDL_x11xinput2.c b/src/video/x11/SDL_x11xinput2.c
index 618eb6fad1..4336854e3c 100644
--- a/src/video/x11/SDL_x11xinput2.c
+++ b/src/video/x11/SDL_x11xinput2.c
@@ -451,7 +451,7 @@ void X11_Xinput2SelectTouch(_THIS, SDL_Window *window)
 #endif
 }
 
-int X11_Xinput2IsInitialized()
+int X11_Xinput2IsInitialized(void)
 {
 #if SDL_VIDEO_DRIVER_X11_XINPUT2
     return xinput2_initialized;
@@ -460,7 +460,7 @@ int X11_Xinput2IsInitialized()
 #endif
 }
 
-int X11_Xinput2IsMultitouchSupported()
+int X11_Xinput2IsMultitouchSupported(void)
 {
 #if SDL_VIDEO_DRIVER_X11_XINPUT2_SUPPORTS_MULTITOUCH
     return xinput2_initialized && xinput2_multitouch_supported;