1 files changed, 43 insertions, 0 deletions
diff --git a/testsuite/tests/deriving/should_compile/T13998.hs b/testsuite/tests/deriving/should_compile/T13998.hs
new file mode 100644
index 0000000000..565d4a35f7
--- /dev/null
+++ b/testsuite/tests/deriving/should_compile/T13998.hs
@@ -0,0 +1,43 @@
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE KindSignatures #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DefaultSignatures #-}
+{-# LANGUAGE GADTs #-}
+
+module T13998 where
+
+import Data.Type.Equality
+
+class EqForall f where
+  eqForall :: f a -> f a -> Bool
+
+class EqForall f => EqForallPoly f where
+  eqForallPoly :: f a -> f b -> Bool
+  default eqForallPoly :: TestEquality f => f a -> f b -> Bool
+  eqForallPoly = defaultEqForallPoly
+
+defaultEqForallPoly :: (TestEquality f, EqForall f) => f a -> f b -> Bool
+defaultEqForallPoly x y = case testEquality x y of
+  Nothing -> False
+  Just Refl -> eqForall x y
+
+
+data Atom = AtomInt | AtomString | AtomBool
+
+data Value (a :: Atom) where
+  ValueInt :: Int -> Value 'AtomInt
+  ValueString :: String -> Value 'AtomString
+  ValueBool :: Bool -> Value 'AtomBool
+
+instance TestEquality Value where
+  testEquality (ValueInt _) (ValueInt _) = Just Refl
+  testEquality (ValueString _) (ValueString _) = Just Refl
+  testEquality (ValueBool _) (ValueBool _) = Just Refl
+  testEquality _ _ = Nothing
+
+instance EqForall Value where
+  eqForall (ValueInt a) (ValueInt b) = a == b
+  eqForall (ValueString a) (ValueString b) = a == b
+  eqForall (ValueBool a) (ValueBool b) = a == b
+
+instance EqForallPoly Value