diff --git a/src/audio/SDL_wave.c b/src/audio/SDL_wave.c
index 465195eb8..48acb3f30 100644
--- a/src/audio/SDL_wave.c
+++ b/src/audio/SDL_wave.c
@@ -440,6 +440,7 @@ SDL_AudioSpec * SDL_LoadWAV_RW (SDL_RWops *src, int freesrc,
 	do {
 		if ( chunk.data != NULL ) {
 			SDL_free(chunk.data);
+			chunk.data = NULL;
 		}
 		lenread = ReadChunk(src, &chunk);
 		if ( lenread < 0 ) {
@@ -522,6 +523,7 @@ SDL_AudioSpec * SDL_LoadWAV_RW (SDL_RWops *src, int freesrc,
 	do {
 		if ( *audio_buf != NULL ) {
 			SDL_free(*audio_buf);
+			*audio_buf = NULL;
 		}
 		lenread = ReadChunk(src, &chunk);
 		if ( lenread < 0 ) {
@@ -591,6 +593,7 @@ static int ReadChunk(SDL_RWops *src, Chunk *chunk)
 	if ( SDL_RWread(src, chunk->data, chunk->length, 1) != 1 ) {
 		SDL_Error(SDL_EFREAD);
 		SDL_free(chunk->data);
+		chunk->data = NULL;
 		return(-1);
 	}
 	return(chunk->length);
diff --git a/src/cdrom/win32/SDL_syscdrom.c b/src/cdrom/win32/SDL_syscdrom.c
index 3d0587dad..98499a88a 100644
--- a/src/cdrom/win32/SDL_syscdrom.c
+++ b/src/cdrom/win32/SDL_syscdrom.c
@@ -377,6 +377,7 @@ void SDL_SYS_CDQuit(void)
 	if ( SDL_numcds > 0 ) {
 		for ( i=0; i<SDL_numcds; ++i ) {
 			SDL_free(SDL_cdlist[i]);
+			SDL_cdlist[i] = NULL;
 		}
 		SDL_numcds = 0;
 	}
diff --git a/src/events/SDL_events.c b/src/events/SDL_events.c
index e246fb78b..290efdf21 100644
--- a/src/events/SDL_events.c
+++ b/src/events/SDL_events.c
@@ -191,9 +191,11 @@ static void SDL_StopEventThread(void)
 		SDL_WaitThread(SDL_EventThread, NULL);
 		SDL_EventThread = NULL;
 		SDL_DestroyMutex(SDL_EventLock.lock);
+		SDL_EventLock.lock = NULL;
 	}
 #ifndef IPOD
 	SDL_DestroyMutex(SDL_EventQ.lock);
+	SDL_EventQ.lock = NULL;
 #endif
 }
 
diff --git a/src/joystick/win32/SDL_mmjoystick.c b/src/joystick/win32/SDL_mmjoystick.c
index e71f8f84d..c12734c4f 100644
--- a/src/joystick/win32/SDL_mmjoystick.c
+++ b/src/joystick/win32/SDL_mmjoystick.c
@@ -344,6 +344,7 @@ void SDL_SYS_JoystickClose(SDL_Joystick *joystick)
 	if (joystick->hwdata != NULL) {
 		/* free system specific hardware data */
 		SDL_free(joystick->hwdata);
+		joystick->hwdata = NULL;
 	}
 }
 
@@ -354,6 +355,7 @@ void SDL_SYS_JoystickQuit(void)
 	for (i = 0; i < MAX_JOYSTICKS; i++) {
 		if ( SYS_JoystickName[i] != NULL ) {
 			SDL_free(SYS_JoystickName[i]);
+			SYS_JoystickName[i] = NULL;
 		}
 	}
 }
diff --git a/src/video/SDL_yuv_sw.c b/src/video/SDL_yuv_sw.c
index 13c4a92e1..303a5e6d4 100644
--- a/src/video/SDL_yuv_sw.c
+++ b/src/video/SDL_yuv_sw.c
@@ -1294,5 +1294,6 @@ void SDL_FreeYUV_SW(_THIS, SDL_Overlay *overlay)
 			SDL_free(swdata->rgb_2_pix);
 		}
 		SDL_free(swdata);
+		overlay->hwdata = NULL;
 	}
 }
diff --git a/src/video/windx5/SDL_dx5yuv.c b/src/video/windx5/SDL_dx5yuv.c
index 2457dacd8..6111ff535 100644
--- a/src/video/windx5/SDL_dx5yuv.c
+++ b/src/video/windx5/SDL_dx5yuv.c
@@ -290,6 +290,7 @@ void DX5_FreeYUVOverlay(_THIS, SDL_Overlay *overlay)
 			IDirectDrawSurface_Release(hwdata->surface);
 		}
 		SDL_free(hwdata);
+		overlay->hwdata = NULL;
 	}
 }