Corrected documentation of SDL_AddTimer() in header file.
diff --git a/include/SDL_timer.h b/include/SDL_timer.h
index 83cd1b3..1f2a020 100644
--- a/include/SDL_timer.h
+++ b/include/SDL_timer.h
@@ -88,7 +88,7 @@ typedef int SDL_TimerID;
/**
* \brief Add a new timer to the pool of timers already running.
*
- * \return A timer ID, or NULL when an error occurs.
+ * \return A timer ID, or 0 when an error occurs.
*/
extern DECLSPEC SDL_TimerID SDLCALL SDL_AddTimer(Uint32 interval,
SDL_TimerCallback callback,