--- haskell-stm-2.1.1.2/Control/Monad/STM.hs.orig	2008-11-01 13:43:37.000000000 -0700
+++ haskell-stm-2.1.1.2/Control/Monad/STM.hs	2010-06-16 14:18:26.365624277 -0700
@@ -41,10 +41,6 @@
 #endif
 
 #ifdef __GLASGOW_HASKELL__
-instance MonadPlus STM where
-  mzero = retry
-  mplus = orElse
-
 check :: Bool -> STM a
 check b = if b then return undefined else retry
 #endif