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diff --git a/testsuite/tests/typecheck/should_compile/T21703.hs b/testsuite/tests/typecheck/should_compile/T21703.hs
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+++ b/testsuite/tests/typecheck/should_compile/T21703.hs
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+{-# LANGUAGE FunctionalDependencies #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+module T21703 where
+
+data Doc
+data Val
+data Head
+
+data EvalM a = EvalM a
+
+class MonadEval head val m | m -> head, head -> val where
+  ret :: a -> m a       
+
+instance MonadEval Head Val EvalM where
+  ret = EvalM
+
+class PrettyM m a where
+  prettyM :: a -> m a
+
+instance PrettyM EvalM Val where
+  prettyM = ret