Index: Modules/_multiprocessing/semaphore.c
===================================================================
--- Modules/_multiprocessing/semaphore.c	(revision 83935)
+++ Modules/_multiprocessing/semaphore.c	(working copy)
@@ -204,6 +204,15 @@
 #ifndef HAVE_SEM_TIMEDWAIT
 #  define sem_timedwait(sem,deadline) sem_timedwait_save(sem,deadline,_save)
 
+/* OS X 10.4 defines SEM_FAILED as -1 instead of (sem_t *)-1;  this gives
+   compliler warnings, and (potentially) undefined behaviour. */
+#ifdef __APPLE__
+#ifdef SEM_FAILED
+#undef SEM_FAILED
+#endif
+#define SEM_FAILED ((sem_t *)-1)
+#endif
+
 int
 sem_timedwait_save(sem_t *sem, struct timespec *deadline, PyThreadState *_save)
 {