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diff --git a/testsuite/tests/indexed-types/should_compile/T2850.hs b/testsuite/tests/indexed-types/should_compile/T2850.hs
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+++ b/testsuite/tests/indexed-types/should_compile/T2850.hs
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+{-# LANGUAGE GeneralizedNewtypeDeriving, TypeFamilies, FlexibleContexts, FlexibleInstances #-}
+
+module T2850 where
+
+class K a where
+  bar :: a -> a
+
+class K (B a) => M a where
+  data B a :: *
+  foo :: B a -> B a
+
+instance M Bool where
+  data B Bool = B1Bool Bool | B2Bool Bool
+  foo = id
+
+instance K (B Bool) where
+  bar = id
+
+instance M Int where
+  newtype B Int = BInt (B Bool) deriving K
+  foo = id