diff --git a/ghc/rts/OSThreads.c b/ghc/rts/OSThreads.c
index abfa5832cf728b384e237615b30f7b02760ab008..01e0a251a1b6afccece1f98e32f7932a35955f33 100644
--- a/ghc/rts/OSThreads.c
+++ b/ghc/rts/OSThreads.c
@@ -186,7 +186,7 @@ createOSThread ( OSThreadId* pId, void (*startProc)(void))
 			   startProcWrapper,
 			   (void*)startProc,
 			   0,
-			   (unsigned*)pId) == NULL);
+			   (unsigned*)pId) == 0);
 }
 
 OSThreadId