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diff --git a/testsuite/tests/typecheck/should_compile/T4401.hs b/testsuite/tests/typecheck/should_compile/T4401.hs
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+++ b/testsuite/tests/typecheck/should_compile/T4401.hs
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+{-# LANGUAGE FlexibleInstances, UndecidableInstances,
+             MultiParamTypeClasses, FunctionalDependencies #-}
+module T4401 where
+
+class Mul x y z | x y -> z
+class IsType a
+class IsType a => IsSized a s | a -> s
+
+data Array n a = Array
+instance IsSized a s => IsType (Array n a)
+instance (IsSized a s, Mul n s ns) => IsSized (Array n a) ns