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diff --git a/testsuite/tests/gadt/CasePrune.hs b/testsuite/tests/gadt/CasePrune.hs
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+{-# LANGUAGE GADTs, GeneralizedNewtypeDeriving #-}
+
+-- See Trac #1251 and the comments
+-- Note [Pruning dead case alternatives] in types/Unify.lhs
+
+module Main( main ) where
+
+data T a where MkT :: T Int
+
+class C a where ic :: T a
+
+instance C Int where ic = MkT
+
+newtype A = MkA Int deriving( C )
+
+-- axiom CoA : A ~ Int
+-- Hence C Int ~ C A
+
+-- instance C A where
+--    ic :: T A
+--    ic = MkT
+
+icA = ic :: T A  -- There are no (non-bot) values of this type
+
+main = print (icA `seq` "ok")
+
+
+