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diff --git a/testsuite/tests/deriving/should_compile/T3965.hs b/testsuite/tests/deriving/should_compile/T3965.hs
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+++ b/testsuite/tests/deriving/should_compile/T3965.hs
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+{-# LANGUAGE DeriveDataTypeable, FlexibleContexts, StandaloneDeriving, TypeOperators, UndecidableInstances #-}
+module T3965 where
+
+import Data.Data
+
+data T f e = Inl (f e) deriving (Data, Eq)
+
+instance (Typeable1 f) => Typeable1 (T f) where
+  typeOf1 _ = error "urk"
+
+newtype Expr f = In (f (Expr f))
+instance Typeable1 f => Typeable (Expr f) where
+  typeOf _ = error "urk"
+
+deriving instance (Typeable1 a, Data (a (Expr a))) => Data (Expr a)
+
+data Var e = Var String deriving (Data, Eq, Typeable)
+
+data Domain e g = Domain
+    (Expr (T Var))
+    deriving (Data, Typeable)
+
+