1 files changed, 27 insertions, 0 deletions
diff --git a/testsuite/tests/indexed-types/should_fail/T14369.hs b/testsuite/tests/indexed-types/should_fail/T14369.hs
new file mode 100644
index 0000000000..ef5166c318
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_fail/T14369.hs
@@ -0,0 +1,27 @@
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilyDependencies #-}
+{-# LANGUAGE DataKinds, PolyKinds #-}
+{-# LANGUAGE TypeOperators #-}
+module T14369 where
+
+data family Sing (a :: k)
+
+data instance Sing (z :: Maybe a) where
+  SNothing :: Sing Nothing
+  SJust :: Sing x -> Sing (Just x)
+
+class SingKind k where
+  type Demote k = r | r -> k
+  fromSing :: Sing (a :: k) -> Demote k
+
+instance SingKind a => SingKind (Maybe a) where
+  type Demote (Maybe a) = Maybe (Demote a)
+  fromSing SNothing = Nothing
+  fromSing (SJust x) = Just (fromSing x)
+
+f :: forall (x :: forall a. Maybe a) a. SingKind a => Sing x -> Maybe (Demote a)
+f = fromSing