diff --git a/Python/thread.c b/Python/thread.c
index f366a71..b5d99ef 100644
--- a/Python/thread.c
+++ b/Python/thread.c
@@ -58,7 +58,7 @@
 #define SUN_LWP
 #endif
 
-#ifdef __MWERKS__
+#if defined(__MWERKS__) && !defined(__BEOS__)
 #define _POSIX_THREADS
 #endif