diff --git a/XMonad/Util/WindowState.hs b/XMonad/Util/WindowState.hs
index 4ffc93ea..45896cbe 100644
--- a/XMonad/Util/WindowState.hs
+++ b/XMonad/Util/WindowState.hs
@@ -1,6 +1,7 @@
 {-#
   LANGUAGE ScopedTypeVariables, GeneralizedNewtypeDeriving,
-  FlexibleInstances, MultiParamTypeClasses
+  FlexibleInstances, MultiParamTypeClasses,
+  FlexibleContexts -- ghc-6.12 only
   #-}
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