diff --git a/src/core/linux/SDL_fcitx.c b/src/core/linux/SDL_fcitx.c
index 792943f70..1519f5c48 100644
--- a/src/core/linux/SDL_fcitx.c
+++ b/src/core/linux/SDL_fcitx.c
@@ -84,7 +84,8 @@ GetAppName()
     return SDL_strdup("SDL_App");
 }
 
-size_t Fcitx_GetPreeditString(SDL_DBusContext *dbus, DBusMessage *msg, char **ret) {
+static size_t
+Fcitx_GetPreeditString(SDL_DBusContext *dbus, DBusMessage *msg, char **ret) {
     char *text = NULL, *subtext;
     size_t text_bytes = 0;
     DBusMessageIter iter, array, sub;
diff --git a/src/core/linux/SDL_ime.c b/src/core/linux/SDL_ime.c
index 7933d49cd..1683c0e06 100644
--- a/src/core/linux/SDL_ime.c
+++ b/src/core/linux/SDL_ime.c
@@ -23,13 +23,13 @@
 #include "SDL_ibus.h"
 #include "SDL_fcitx.h"
 
-typedef SDL_bool (*_SDL_IME_Init)();
-typedef void (*_SDL_IME_Quit)();
+typedef SDL_bool (*_SDL_IME_Init)(void);
+typedef void (*_SDL_IME_Quit)(void);
 typedef void (*_SDL_IME_SetFocus)(SDL_bool);
-typedef void (*_SDL_IME_Reset)();
+typedef void (*_SDL_IME_Reset)(void);
 typedef SDL_bool (*_SDL_IME_ProcessKeyEvent)(Uint32, Uint32);
 typedef void (*_SDL_IME_UpdateTextRect)(SDL_Rect *);
-typedef void (*_SDL_IME_PumpEvents)();
+typedef void (*_SDL_IME_PumpEvents)(void);
 
 static _SDL_IME_Init SDL_IME_Init_Real = NULL;
 static _SDL_IME_Quit SDL_IME_Quit_Real = NULL;
diff --git a/src/misc/unix/SDL_sysurl.c b/src/misc/unix/SDL_sysurl.c
index 198b425e8..016381393 100644
--- a/src/misc/unix/SDL_sysurl.c
+++ b/src/misc/unix/SDL_sysurl.c
@@ -65,8 +65,6 @@ SDL_SYS_OpenURL(const char *url)
             return SDL_SetError("Waiting on xdg-open failed: %s", strerror(errno));
         }
     }
-
-    return 0;
 }
 
 /* vi: set ts=4 sw=4 expandtab: */
diff --git a/src/test/SDL_test_random.c b/src/test/SDL_test_random.c
index 009e23d3b..af4e4573b 100644
--- a/src/test/SDL_test_random.c
+++ b/src/test/SDL_test_random.c
@@ -83,7 +83,8 @@ unsigned int SDLTest_Random(SDLTest_RandomContext * rndContext)
 
   if (rndContext==NULL) return -1;
 
-  xh = rndContext->x >> 16, xl = rndContext->x & 65535;
+  xh = rndContext->x >> 16;
+  xl = rndContext->x & 65535;
   rndContext->x = rndContext->x * rndContext->a + rndContext->c;
   rndContext->c =
     xh * rndContext->ah + ((xh * rndContext->al) >> 16) +
diff --git a/src/video/kmsdrm/SDL_kmsdrmmouse.c b/src/video/kmsdrm/SDL_kmsdrmmouse.c
index 08e51aea4..b45909027 100644
--- a/src/video/kmsdrm/SDL_kmsdrmmouse.c
+++ b/src/video/kmsdrm/SDL_kmsdrmmouse.c
@@ -119,7 +119,7 @@ KMSDRM_CreateCursorBO (SDL_VideoDisplay *display) {
 } 
 
 /* Remove a cursor buffer from a display's DRM cursor BO. */
-int
+static int
 KMSDRM_RemoveCursorFromBO(SDL_VideoDisplay *display)
 {
     int ret = 0;
@@ -138,7 +138,7 @@ KMSDRM_RemoveCursorFromBO(SDL_VideoDisplay *display)
 }
 
 /* Dump a cursor buffer to a display's DRM cursor BO.  */
-int
+static int
 KMSDRM_DumpCursorToBO(SDL_VideoDisplay *display, SDL_Cursor *cursor)
 {
     SDL_DisplayData *dispdata = (SDL_DisplayData *) display->driverdata;
@@ -403,8 +403,6 @@ KMSDRM_WarpMouseGlobal(int x, int y)
     } else {
         return SDL_SetError("No mouse or current cursor.");
     }
-
-    return 0;
 }
 
 void
diff --git a/src/video/kmsdrm/SDL_kmsdrmmouse.h b/src/video/kmsdrm/SDL_kmsdrmmouse.h
index 36625acdb..8bef48b00 100644
--- a/src/video/kmsdrm/SDL_kmsdrmmouse.h
+++ b/src/video/kmsdrm/SDL_kmsdrmmouse.h
@@ -48,7 +48,7 @@ extern void KMSDRM_QuitMouse(_THIS);
 
 extern void KMSDRM_CreateCursorBO(SDL_VideoDisplay *display);
 extern void KMSDRM_DestroyCursorBO(_THIS, SDL_VideoDisplay *display);
-extern void KMSDRM_InitCursor();
+extern void KMSDRM_InitCursor(void);
 
 #endif /* SDL_KMSDRM_mouse_h_ */
 
diff --git a/src/video/kmsdrm/SDL_kmsdrmvideo.c b/src/video/kmsdrm/SDL_kmsdrmvideo.c
index 9b7160918..dbc1b4455 100644
--- a/src/video/kmsdrm/SDL_kmsdrmvideo.c
+++ b/src/video/kmsdrm/SDL_kmsdrmvideo.c
@@ -471,7 +471,7 @@ KMSDRM_WaitPageflip(_THIS, SDL_WindowData *windata) {
    available on the DRM connector of the display.
    We use the SDL mode list (which we filled in KMSDRM_GetDisplayModes)
    because it's ordered, while the list on the connector is mostly random.*/
-drmModeModeInfo*
+static drmModeModeInfo*
 KMSDRM_GetClosestDisplayMode(SDL_VideoDisplay * display,
 uint32_t width, uint32_t height, uint32_t refresh_rate){
 
@@ -502,7 +502,8 @@ uint32_t width, uint32_t height, uint32_t refresh_rate){
 /*****************************************************************************/
 
 /* Deinitializes the driverdata of the SDL Displays in the SDL display list. */
-void KMSDRM_DeinitDisplays (_THIS) {
+static void
+KMSDRM_DeinitDisplays (_THIS) {
 
     SDL_DisplayData *dispdata;
     int num_displays, i;
@@ -531,7 +532,8 @@ void KMSDRM_DeinitDisplays (_THIS) {
 
 /* Gets a DRM connector, builds an SDL_Display with it, and adds it to the
    list of SDL Displays in _this->displays[]  */
-void KMSDRM_AddDisplay (_THIS, drmModeConnector *connector, drmModeRes *resources) {
+static void
+KMSDRM_AddDisplay (_THIS, drmModeConnector *connector, drmModeRes *resources) {
 
     SDL_VideoData *viddata = ((SDL_VideoData *)_this->driverdata);
     SDL_DisplayData *dispdata = NULL;
@@ -719,7 +721,8 @@ cleanup:
    closed when we get to the end of this function.
    This is to be called early, in VideoInit(), because it gets us
    the videomode information, which SDL needs immediately after VideoInit(). */
-int KMSDRM_InitDisplays (_THIS) {
+static int
+KMSDRM_InitDisplays (_THIS) {
 
     SDL_VideoData *viddata = ((SDL_VideoData *)_this->driverdata);
     drmModeRes *resources = NULL;
@@ -813,7 +816,7 @@ cleanup:
    These things are incompatible with Vulkan, which accesses the same resources
    internally so they must be free when trying to build a Vulkan surface.
 */
-int
+static int
 KMSDRM_GBMInit (_THIS, SDL_DisplayData *dispdata)
 {
     SDL_VideoData *viddata = (SDL_VideoData *)_this->driverdata;
@@ -837,7 +840,7 @@ KMSDRM_GBMInit (_THIS, SDL_DisplayData *dispdata)
 }
 
 /* Deinit the Vulkan-incompatible KMSDRM stuff. */
-void
+static void
 KMSDRM_GBMDeinit (_THIS, SDL_DisplayData *dispdata)
 {
     SDL_VideoData *viddata = ((SDL_VideoData *)_this->driverdata);
@@ -858,7 +861,7 @@ KMSDRM_GBMDeinit (_THIS, SDL_DisplayData *dispdata)
     viddata->gbm_init = SDL_FALSE;
 }
 
-void
+static void
 KMSDRM_DestroySurfaces(_THIS, SDL_Window *window)
 {
     SDL_VideoData *viddata = ((SDL_VideoData *)_this->driverdata);
diff --git a/src/video/kmsdrm/SDL_kmsdrmvulkan.c b/src/video/kmsdrm/SDL_kmsdrmvulkan.c
index 390271e34..2a5897afb 100644
--- a/src/video/kmsdrm/SDL_kmsdrmvulkan.c
+++ b/src/video/kmsdrm/SDL_kmsdrmvulkan.c
@@ -182,7 +182,7 @@ SDL_bool KMSDRM_Vulkan_CreateSurface(_THIS,
                                   VkInstance instance,
                                   VkSurfaceKHR *surface)
 {
-    VkPhysicalDevice gpu;
+    VkPhysicalDevice gpu = NULL;
     uint32_t gpu_count;
     uint32_t display_count;
     uint32_t mode_count;
diff --git a/src/video/wayland/SDL_waylandclipboard.c b/src/video/wayland/SDL_waylandclipboard.c
index 789273b53..f43f63f83 100644
--- a/src/video/wayland/SDL_waylandclipboard.c
+++ b/src/video/wayland/SDL_waylandclipboard.c
@@ -24,6 +24,7 @@
 
 #include "SDL_waylanddatamanager.h"
 #include "SDL_waylandevents_c.h"
+#include "SDL_waylandclipboard.h"
 
 int
 Wayland_SetClipboardText(_THIS, const char *text)
diff --git a/src/video/wayland/SDL_waylandmessagebox.c b/src/video/wayland/SDL_waylandmessagebox.c
index a612ef74c..c9a6563a0 100644
--- a/src/video/wayland/SDL_waylandmessagebox.c
+++ b/src/video/wayland/SDL_waylandmessagebox.c
@@ -31,6 +31,8 @@
 #include <string.h> /* strerr */
 #include <errno.h>
 
+#include "SDL_waylandmessagebox.h"
+
 #define MAX_BUTTONS             8       /* Maximum number of buttons supported */
 
 int
@@ -186,7 +188,6 @@ Wayland_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
             return SDL_SetError("Waiting on zenity failed: %s", strerror(errno));
         }
     }
-    return 0;
 }
 
 #endif /* SDL_VIDEO_DRIVER_WAYLAND */
diff --git a/src/video/wayland/SDL_waylandmouse.c b/src/video/wayland/SDL_waylandmouse.c
index 67ab721ee..73f6a5030 100644
--- a/src/video/wayland/SDL_waylandmouse.c
+++ b/src/video/wayland/SDL_waylandmouse.c
@@ -38,7 +38,7 @@
 #include "SDL_waylandevents_c.h"
 
 #include "wayland-cursor.h"
-
+#include "SDL_waylandmouse.h"
 
 
 typedef struct {
diff --git a/src/video/x11/SDL_x11window.c b/src/video/x11/SDL_x11window.c
index 1b3e693ad..8c0d31d38 100644
--- a/src/video/x11/SDL_x11window.c
+++ b/src/video/x11/SDL_x11window.c
@@ -1693,7 +1693,7 @@ X11_SetWindowMouseGrab(_THIS, SDL_Window * window, SDL_bool grabbed)
         if (!data->videodata->broken_pointer_grab) {
             const unsigned int mask = ButtonPressMask | ButtonReleaseMask | PointerMotionMask | FocusChangeMask;
             int attempts;
-            int result;
+            int result = 0;
 
             /* Try for up to 5000ms (5s) to grab. If it still fails, stop trying. */
             for (attempts = 0; attempts < 100; attempts++) {