diff --git a/src/haptic/darwin/SDL_syshaptic.c b/src/haptic/darwin/SDL_syshaptic.c
index d662012c3..013ae40f9 100644
--- a/src/haptic/darwin/SDL_syshaptic.c
+++ b/src/haptic/darwin/SDL_syshaptic.c
@@ -189,7 +189,7 @@ SDL_SYS_HapticInit(void)
 }
 
 int
-SDL_SYS_NumHaptics()
+SDL_SYS_NumHaptics(void)
 {
     return numhaptics;
 }
diff --git a/src/haptic/linux/SDL_syshaptic.c b/src/haptic/linux/SDL_syshaptic.c
index 7bd966449..ae7f852ad 100644
--- a/src/haptic/linux/SDL_syshaptic.c
+++ b/src/haptic/linux/SDL_syshaptic.c
@@ -187,7 +187,7 @@ SDL_SYS_HapticInit(void)
 }
 
 int
-SDL_SYS_NumHaptics()
+SDL_SYS_NumHaptics(void)
 {
     return numhaptics;
 }
diff --git a/src/haptic/windows/SDL_windowshaptic.c b/src/haptic/windows/SDL_windowshaptic.c
index c6bcba1f3..9a321c507 100644
--- a/src/haptic/windows/SDL_windowshaptic.c
+++ b/src/haptic/windows/SDL_windowshaptic.c
@@ -98,7 +98,7 @@ SDL_SYS_RemoveHapticDevice(SDL_hapticlist_item *prev, SDL_hapticlist_item *item)
 }
 
 int
-SDL_SYS_NumHaptics()
+SDL_SYS_NumHaptics(void)
 {
     return numhaptics;
 }
diff --git a/src/joystick/android/SDL_sysjoystick.c b/src/joystick/android/SDL_sysjoystick.c
index a09e9a12c..cbc921082 100644
--- a/src/joystick/android/SDL_sysjoystick.c
+++ b/src/joystick/android/SDL_sysjoystick.c
@@ -363,12 +363,14 @@ SDL_SYS_JoystickInit(void)
 
 }
 
-int SDL_SYS_NumJoysticks()
+int
+SDL_SYS_NumJoysticks(void)
 {
     return numjoysticks;
 }
 
-void SDL_SYS_JoystickDetect()
+void
+SDL_SYS_JoystickDetect(void)
 {
     /* Support for device connect/disconnect is API >= 16 only,
      * so we poll every three seconds
diff --git a/src/joystick/bsd/SDL_sysjoystick.c b/src/joystick/bsd/SDL_sysjoystick.c
index ddc899f6e..d72d22d6b 100644
--- a/src/joystick/bsd/SDL_sysjoystick.c
+++ b/src/joystick/bsd/SDL_sysjoystick.c
@@ -204,12 +204,14 @@ SDL_SYS_JoystickInit(void)
     return (SDL_SYS_numjoysticks);
 }
 
-int SDL_SYS_NumJoysticks()
+int
+SDL_SYS_NumJoysticks(void)
 {
     return SDL_SYS_numjoysticks;
 }
 
-void SDL_SYS_JoystickDetect()
+void
+SDL_SYS_JoystickDetect(void)
 {
 }
 
diff --git a/src/joystick/darwin/SDL_sysjoystick.c b/src/joystick/darwin/SDL_sysjoystick.c
index 5b48b9fbb..b4a824bd7 100644
--- a/src/joystick/darwin/SDL_sysjoystick.c
+++ b/src/joystick/darwin/SDL_sysjoystick.c
@@ -580,7 +580,7 @@ SDL_SYS_JoystickInit(void)
 
 /* Function to return the number of joystick devices plugged in right now */
 int
-SDL_SYS_NumJoysticks()
+SDL_SYS_NumJoysticks(void)
 {
     recDevice *device = gpDeviceList;
     int nJoySticks = 0;
@@ -598,7 +598,7 @@ SDL_SYS_NumJoysticks()
 /* Function to cause any queued joystick insertions to be processed
  */
 void
-SDL_SYS_JoystickDetect()
+SDL_SYS_JoystickDetect(void)
 {
     recDevice *device = gpDeviceList;
     while (device) {
diff --git a/src/joystick/dummy/SDL_sysjoystick.c b/src/joystick/dummy/SDL_sysjoystick.c
index 10fda10da..edd8bdc36 100644
--- a/src/joystick/dummy/SDL_sysjoystick.c
+++ b/src/joystick/dummy/SDL_sysjoystick.c
@@ -37,12 +37,14 @@ SDL_SYS_JoystickInit(void)
     return 0;
 }
 
-int SDL_SYS_NumJoysticks()
+int
+SDL_SYS_NumJoysticks(void)
 {
     return 0;
 }
 
-void SDL_SYS_JoystickDetect()
+void
+SDL_SYS_JoystickDetect(void)
 {
 }
 
diff --git a/src/joystick/emscripten/SDL_sysjoystick.c b/src/joystick/emscripten/SDL_sysjoystick.c
index 6b203667a..75d88fd0d 100644
--- a/src/joystick/emscripten/SDL_sysjoystick.c
+++ b/src/joystick/emscripten/SDL_sysjoystick.c
@@ -240,12 +240,14 @@ JoystickByIndex(int index)
     return item;
 }
 
-int SDL_SYS_NumJoysticks()
+int
+SDL_SYS_NumJoysticks(void)
 {
     return numjoysticks;
 }
 
-void SDL_SYS_JoystickDetect()
+void
+SDL_SYS_JoystickDetect(void)
 {
 }
 
diff --git a/src/joystick/haiku/SDL_haikujoystick.cc b/src/joystick/haiku/SDL_haikujoystick.cc
index a680189c7..13bc6c62c 100644
--- a/src/joystick/haiku/SDL_haikujoystick.cc
+++ b/src/joystick/haiku/SDL_haikujoystick.cc
@@ -84,12 +84,12 @@ extern "C"
         return (SDL_SYS_numjoysticks);
     }
 
-    int SDL_SYS_NumJoysticks()
+    int SDL_SYS_NumJoysticks(void)
     {
         return SDL_SYS_numjoysticks;
     }
 
-    void SDL_SYS_JoystickDetect()
+    void SDL_SYS_JoystickDetect(void)
     {
     }
 
diff --git a/src/joystick/iphoneos/SDL_sysjoystick.m b/src/joystick/iphoneos/SDL_sysjoystick.m
index eb7e00032..893f62736 100644
--- a/src/joystick/iphoneos/SDL_sysjoystick.m
+++ b/src/joystick/iphoneos/SDL_sysjoystick.m
@@ -326,12 +326,14 @@ SDL_SYS_JoystickInit(void)
     return numjoysticks;
 }
 
-int SDL_SYS_NumJoysticks()
+int
+SDL_SYS_NumJoysticks(void)
 {
     return numjoysticks;
 }
 
-void SDL_SYS_JoystickDetect()
+void
+SDL_SYS_JoystickDetect(void)
 {
 }
 
diff --git a/src/joystick/linux/SDL_sysjoystick.c b/src/joystick/linux/SDL_sysjoystick.c
index e4f01a33d..1621474d0 100644
--- a/src/joystick/linux/SDL_sysjoystick.c
+++ b/src/joystick/linux/SDL_sysjoystick.c
@@ -348,12 +348,14 @@ SDL_SYS_JoystickInit(void)
 #endif
 }
 
-int SDL_SYS_NumJoysticks()
+int
+SDL_SYS_NumJoysticks(void)
 {
     return numjoysticks;
 }
 
-void SDL_SYS_JoystickDetect()
+void
+SDL_SYS_JoystickDetect(void)
 {
 #if SDL_USE_LIBUDEV
     SDL_UDEV_Poll();
diff --git a/src/joystick/psp/SDL_sysjoystick.c b/src/joystick/psp/SDL_sysjoystick.c
index 352960edf..9f3150d5e 100644
--- a/src/joystick/psp/SDL_sysjoystick.c
+++ b/src/joystick/psp/SDL_sysjoystick.c
@@ -132,12 +132,12 @@ int SDL_SYS_JoystickInit(void)
     return 1;
 }
 
-int SDL_SYS_NumJoysticks()
+int SDL_SYS_NumJoysticks(void)
 {
     return 1;
 }
 
-void SDL_SYS_JoystickDetect()
+void SDL_SYS_JoystickDetect(void)
 {
 }
 
diff --git a/src/joystick/windows/SDL_mmjoystick.c b/src/joystick/windows/SDL_mmjoystick.c
index 374618181..e61756121 100644
--- a/src/joystick/windows/SDL_mmjoystick.c
+++ b/src/joystick/windows/SDL_mmjoystick.c
@@ -183,12 +183,14 @@ SDL_SYS_JoystickInit(void)
     return (SDL_SYS_numjoysticks);
 }
 
-int SDL_SYS_NumJoysticks()
+int
+SDL_SYS_NumJoysticks(void)
 {
     return SDL_SYS_numjoysticks;
 }
 
-void SDL_SYS_JoystickDetect()
+void
+SDL_SYS_JoystickDetect(void)
 {
 }
 
diff --git a/src/joystick/windows/SDL_windowsjoystick.c b/src/joystick/windows/SDL_windowsjoystick.c
index e528afa7f..f965753a8 100644
--- a/src/joystick/windows/SDL_windowsjoystick.c
+++ b/src/joystick/windows/SDL_windowsjoystick.c
@@ -307,7 +307,7 @@ SDL_SYS_JoystickInit(void)
 
 /* return the number of joysticks that are connected right now */
 int
-SDL_SYS_NumJoysticks()
+SDL_SYS_NumJoysticks(void)
 {
     int nJoysticks = 0;
     JoyStick_DeviceData *device = SYS_Joystick;
@@ -321,7 +321,7 @@ SDL_SYS_NumJoysticks()
 
 /* detect any new joysticks being inserted into the system */
 void
-SDL_SYS_JoystickDetect()
+SDL_SYS_JoystickDetect(void)
 {
     JoyStick_DeviceData *pCurList = NULL;
 
diff --git a/src/render/opengl/SDL_shaders_gl.c b/src/render/opengl/SDL_shaders_gl.c
index bcf7b4315..9eeb05189 100644
--- a/src/render/opengl/SDL_shaders_gl.c
+++ b/src/render/opengl/SDL_shaders_gl.c
@@ -369,7 +369,7 @@ DestroyShaderProgram(GL_ShaderContext *ctx, GL_ShaderData *data)
 }
 
 GL_ShaderContext *
-GL_CreateShaderContext()
+GL_CreateShaderContext(void)
 {
     GL_ShaderContext *ctx;
     SDL_bool shaders_supported;
diff --git a/src/thread/SDL_thread.c b/src/thread/SDL_thread.c
index ae865790a..db7204fce 100644
--- a/src/thread/SDL_thread.c
+++ b/src/thread/SDL_thread.c
@@ -121,7 +121,7 @@ static SDL_TLSEntry *SDL_generic_TLS;
 
 
 SDL_TLSData *
-SDL_Generic_GetTLSData()
+SDL_Generic_GetTLSData(void)
 {
     SDL_threadID thread = SDL_ThreadID();
     SDL_TLSEntry *entry;
diff --git a/src/thread/generic/SDL_systls.c b/src/thread/generic/SDL_systls.c
index e29c19818..19dc8a4d8 100644
--- a/src/thread/generic/SDL_systls.c
+++ b/src/thread/generic/SDL_systls.c
@@ -24,7 +24,7 @@
 
 
 SDL_TLSData *
-SDL_SYS_GetTLSData()
+SDL_SYS_GetTLSData(void)
 {
     return SDL_Generic_GetTLSData();
 }
diff --git a/src/thread/pthread/SDL_systls.c b/src/thread/pthread/SDL_systls.c
index ba8503663..04edc49f9 100644
--- a/src/thread/pthread/SDL_systls.c
+++ b/src/thread/pthread/SDL_systls.c
@@ -32,7 +32,7 @@ static pthread_key_t thread_local_storage = INVALID_PTHREAD_KEY;
 static SDL_bool generic_local_storage = SDL_FALSE;
 
 SDL_TLSData *
-SDL_SYS_GetTLSData()
+SDL_SYS_GetTLSData(void)
 {
     if (thread_local_storage == INVALID_PTHREAD_KEY && !generic_local_storage) {
         static SDL_SpinLock lock;
diff --git a/src/thread/stdcpp/SDL_systhread.cpp b/src/thread/stdcpp/SDL_systhread.cpp
index 6e5ef473e..874bdd732 100644
--- a/src/thread/stdcpp/SDL_systhread.cpp
+++ b/src/thread/stdcpp/SDL_systhread.cpp
@@ -153,7 +153,7 @@ SDL_SYS_DetachThread(SDL_Thread * thread)
 
 extern "C"
 SDL_TLSData *
-SDL_SYS_GetTLSData()
+SDL_SYS_GetTLSData(void)
 {
     return SDL_Generic_GetTLSData();
 }
diff --git a/src/thread/windows/SDL_systls.c b/src/thread/windows/SDL_systls.c
index 7ec630e8f..800e94a2b 100644
--- a/src/thread/windows/SDL_systls.c
+++ b/src/thread/windows/SDL_systls.c
@@ -32,7 +32,7 @@ static DWORD thread_local_storage = TLS_OUT_OF_INDEXES;
 static SDL_bool generic_local_storage = SDL_FALSE;
 
 SDL_TLSData *
-SDL_SYS_GetTLSData()
+SDL_SYS_GetTLSData(void)
 {
     if (thread_local_storage == TLS_OUT_OF_INDEXES && !generic_local_storage) {
         static SDL_SpinLock lock;