diff --git a/Xcode-iOS/Demos/src/common.c b/Xcode-iOS/Demos/src/common.c
index 0a1485ae9..e15fb5ff1 100644
--- a/Xcode-iOS/Demos/src/common.c
+++ b/Xcode-iOS/Demos/src/common.c
@@ -39,7 +39,7 @@ fatalError(const char *string)
 static Uint64 prevTime = 0;
 
 double
-updateDeltaTime()
+updateDeltaTime(void)
 {
     Uint64 curTime;
     double deltaTime;
diff --git a/Xcode-iOS/Demos/src/common.h b/Xcode-iOS/Demos/src/common.h
index 96b2c964a..60475086e 100644
--- a/Xcode-iOS/Demos/src/common.h
+++ b/Xcode-iOS/Demos/src/common.h
@@ -7,4 +7,4 @@
 extern int randomInt(int min, int max);
 extern float randomFloat(float min, float max);
 extern void fatalError(const char *string);
-extern double updateDeltaTime();
+extern double updateDeltaTime(void);
diff --git a/include/SDL_atomic.h b/include/SDL_atomic.h
index 5ff963241..580e0414f 100644
--- a/include/SDL_atomic.h
+++ b/include/SDL_atomic.h
@@ -159,8 +159,8 @@ void _ReadWriteBarrier(void);
 #elif defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6T2__) || defined(__ARM_ARCH_6Z__) || defined(__ARM_ARCH_6ZK__)
 #ifdef __thumb__
 /* The mcr instruction isn't available in thumb mode, use real functions */
-extern DECLSPEC void SDLCALL SDL_MemoryBarrierRelease();
-extern DECLSPEC void SDLCALL SDL_MemoryBarrierAcquire();
+extern DECLSPEC void SDLCALL SDL_MemoryBarrierRelease(void);
+extern DECLSPEC void SDLCALL SDL_MemoryBarrierAcquire(void);
 #else
 #define SDL_MemoryBarrierRelease()   __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
 #define SDL_MemoryBarrierAcquire()   __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
diff --git a/include/SDL_gamecontroller.h b/include/SDL_gamecontroller.h
index 56051a831..36af08dbe 100644
--- a/include/SDL_gamecontroller.h
+++ b/include/SDL_gamecontroller.h
@@ -140,7 +140,7 @@ extern DECLSPEC int SDLCALL SDL_GameControllerAddMapping(const char* mappingStri
  *
  *  \return the number of mappings
  */
-extern DECLSPEC int SDLCALL SDL_GameControllerNumMappings();
+extern DECLSPEC int SDLCALL SDL_GameControllerNumMappings(void);
 
 /**
  *  Get the mapping at a particular index.
diff --git a/src/core/linux/SDL_fcitx.c b/src/core/linux/SDL_fcitx.c
index 83d19e690..a4bc404c8 100644
--- a/src/core/linux/SDL_fcitx.c
+++ b/src/core/linux/SDL_fcitx.c
@@ -535,7 +535,7 @@ SDL_Fcitx_UpdateTextRect(SDL_Rect *rect)
 }
 
 void
-SDL_Fcitx_PumpEvents()
+SDL_Fcitx_PumpEvents(void)
 {
     SDL_DBusContext *dbus = fcitx_client.dbus;
     DBusConnection *conn = dbus->session_conn;
diff --git a/src/core/linux/SDL_fcitx.h b/src/core/linux/SDL_fcitx.h
index c0d822adb..e3148ea48 100644
--- a/src/core/linux/SDL_fcitx.h
+++ b/src/core/linux/SDL_fcitx.h
@@ -33,7 +33,7 @@ extern void SDL_Fcitx_SetFocus(SDL_bool focused);
 extern void SDL_Fcitx_Reset(void);
 extern SDL_bool SDL_Fcitx_ProcessKeyEvent(Uint32 keysym, Uint32 keycode);
 extern void SDL_Fcitx_UpdateTextRect(SDL_Rect *rect);
-extern void SDL_Fcitx_PumpEvents();
+extern void SDL_Fcitx_PumpEvents(void);
 
 #endif /* SDL_fcitx_h_ */
 
diff --git a/src/core/linux/SDL_ibus.h b/src/core/linux/SDL_ibus.h
index bd22a88e3..d05e4ea8f 100644
--- a/src/core/linux/SDL_ibus.h
+++ b/src/core/linux/SDL_ibus.h
@@ -49,7 +49,7 @@ extern void SDL_IBus_UpdateTextRect(SDL_Rect *window_relative_rect);
 
 /* Checks DBus for new IBus events, and calls SDL_SendKeyboardText / 
    SDL_SendEditingText for each event it finds */
-extern void SDL_IBus_PumpEvents();
+extern void SDL_IBus_PumpEvents(void);
 
 #endif /* HAVE_IBUS_IBUS_H */
 
diff --git a/src/core/windows/SDL_windows.c b/src/core/windows/SDL_windows.c
index 6433fe26f..676fadce7 100644
--- a/src/core/windows/SDL_windows.c
+++ b/src/core/windows/SDL_windows.c
@@ -115,7 +115,7 @@ IsWindowsVersionOrGreater(WORD wMajorVersion, WORD wMinorVersion, WORD wServiceP
 }
 #endif
 
-BOOL WIN_IsWindowsVistaOrGreater()
+BOOL WIN_IsWindowsVistaOrGreater(void)
 {
 #ifdef __WINRT__
     return TRUE;
diff --git a/src/core/windows/SDL_windows.h b/src/core/windows/SDL_windows.h
index 0f67e4be5..6a63c08ba 100644
--- a/src/core/windows/SDL_windows.h
+++ b/src/core/windows/SDL_windows.h
@@ -57,7 +57,7 @@ extern HRESULT WIN_CoInitialize(void);
 extern void WIN_CoUninitialize(void);
 
 /* Returns SDL_TRUE if we're running on Windows Vista and newer */
-extern BOOL WIN_IsWindowsVistaOrGreater();
+extern BOOL WIN_IsWindowsVistaOrGreater(void);
 
 /* You need to SDL_free() the result of this call. */
 extern char *WIN_LookupAudioDeviceName(const WCHAR *name, const GUID *guid);
diff --git a/src/joystick/SDL_gamecontroller.c b/src/joystick/SDL_gamecontroller.c
index a9c8e826d..598d4643d 100644
--- a/src/joystick/SDL_gamecontroller.c
+++ b/src/joystick/SDL_gamecontroller.c
@@ -891,7 +891,7 @@ SDL_GameControllerAddMapping(const char *mappingString)
  *  Get the number of mappings installed
  */
 int
-SDL_GameControllerNumMappings()
+SDL_GameControllerNumMappings(void)
 {
     int num_mappings = 0;
     ControllerMapping_t *mapping;
diff --git a/src/video/haiku/SDL_bkeyboard.cc b/src/video/haiku/SDL_bkeyboard.cc
index 6880dae28..3f81b4060 100644
--- a/src/video/haiku/SDL_bkeyboard.cc
+++ b/src/video/haiku/SDL_bkeyboard.cc
@@ -41,7 +41,7 @@ extern "C" {
 static SDL_Scancode keymap[KEYMAP_SIZE];
 static int8 keystate[KEYMAP_SIZE];
 
-void BE_InitOSKeymap() {
+void BE_InitOSKeymap(void) {
 		for( uint i = 0; i < SDL_TABLESIZE(keymap); ++i ) {
 			keymap[i] = SDL_SCANCODE_UNKNOWN;
 		}
diff --git a/src/video/haiku/SDL_bkeyboard.h b/src/video/haiku/SDL_bkeyboard.h
index 84621e26e..90f4b2f8a 100644
--- a/src/video/haiku/SDL_bkeyboard.h
+++ b/src/video/haiku/SDL_bkeyboard.h
@@ -30,7 +30,7 @@ extern "C" {
 
 #include "../../../include/SDL_keyboard.h"
 
-extern void BE_InitOSKeymap();
+extern void BE_InitOSKeymap(void);
 extern SDL_Scancode BE_GetScancodeFromBeKey(int32 bkey);
 extern int8 BE_GetKeyState(int32 bkey);
 extern void BE_SetKeyState(int32 bkey, int8 state);
diff --git a/src/video/uikit/SDL_uikitmessagebox.h b/src/video/uikit/SDL_uikitmessagebox.h
index 528072413..6b9746486 100644
--- a/src/video/uikit/SDL_uikitmessagebox.h
+++ b/src/video/uikit/SDL_uikitmessagebox.h
@@ -22,7 +22,7 @@
 
 #if SDL_VIDEO_DRIVER_UIKIT
 
-extern SDL_bool UIKit_ShowingMessageBox();
+extern SDL_bool UIKit_ShowingMessageBox(void);
 
 extern int UIKit_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid);
 
diff --git a/src/video/uikit/SDL_uikitmessagebox.m b/src/video/uikit/SDL_uikitmessagebox.m
index 5778032a0..5864e7178 100644
--- a/src/video/uikit/SDL_uikitmessagebox.m
+++ b/src/video/uikit/SDL_uikitmessagebox.m
@@ -31,7 +31,7 @@
 static SDL_bool s_showingMessageBox = SDL_FALSE;
 
 SDL_bool
-UIKit_ShowingMessageBox()
+UIKit_ShowingMessageBox(void)
 {
     return s_showingMessageBox;
 }
diff --git a/src/video/uikit/SDL_uikitopengles.h b/src/video/uikit/SDL_uikitopengles.h
index e1c78a4d3..4d12bca49 100644
--- a/src/video/uikit/SDL_uikitopengles.h
+++ b/src/video/uikit/SDL_uikitopengles.h
@@ -33,7 +33,7 @@ extern void UIKit_GL_DeleteContext(_THIS, SDL_GLContext context);
 extern void *UIKit_GL_GetProcAddress(_THIS, const char *proc);
 extern int UIKit_GL_LoadLibrary(_THIS, const char *path);
 
-extern void UIKit_GL_RestoreCurrentContext();
+extern void UIKit_GL_RestoreCurrentContext(void);
 
 #endif
 
diff --git a/src/video/uikit/SDL_uikitopengles.m b/src/video/uikit/SDL_uikitopengles.m
index 1ce138640..c0e129936 100644
--- a/src/video/uikit/SDL_uikitopengles.m
+++ b/src/video/uikit/SDL_uikitopengles.m
@@ -228,7 +228,7 @@ UIKit_GL_DeleteContext(_THIS, SDL_GLContext context)
 }
 
 void
-UIKit_GL_RestoreCurrentContext()
+UIKit_GL_RestoreCurrentContext(void)
 {
     @autoreleasepool {
         /* Some iOS system functionality (such as Dictation on the on-screen
diff --git a/src/video/winrt/SDL_winrtevents.cpp b/src/video/winrt/SDL_winrtevents.cpp
index 30cf01633..85b56b35e 100644
--- a/src/video/winrt/SDL_winrtevents.cpp
+++ b/src/video/winrt/SDL_winrtevents.cpp
@@ -105,7 +105,7 @@ WINRT_XAMLThreadMain(void * userdata)
 }
 
 void
-WINRT_CycleXAMLThread()
+WINRT_CycleXAMLThread(void)
 {
     switch (_threadState) {
         case ThreadState_NotLaunched:
diff --git a/src/video/winrt/SDL_winrtevents_c.h b/src/video/winrt/SDL_winrtevents_c.h
index 05a90a3bf..98ed433e9 100644
--- a/src/video/winrt/SDL_winrtevents_c.h
+++ b/src/video/winrt/SDL_winrtevents_c.h
@@ -75,7 +75,7 @@ extern SDL_bool WINRT_IsScreenKeyboardShown(_THIS, SDL_Window *window);
 #endif  // NTDDI_VERSION >= ...
 
 /* XAML Thread Management */
-extern void WINRT_CycleXAMLThread();
+extern void WINRT_CycleXAMLThread(void);
 
 #endif // ifdef __cplusplus_winrt