1 files changed, 23 insertions, 0 deletions
diff --git a/testsuite/tests/simplCore/should_compile/T22459.hs b/testsuite/tests/simplCore/should_compile/T22459.hs
new file mode 100644
index 0000000000..be28c5e2c0
--- /dev/null
+++ b/testsuite/tests/simplCore/should_compile/T22459.hs
@@ -0,0 +1,23 @@
+{-# LANGUAGE UndecidableInstances #-}
+
+{-# OPTIONS_GHC -O #-}
+
+module Lib (foo) where
+
+import qualified Data.Map as M
+
+newtype Fix f = Fix (f (Fix f))
+
+instance Eq (f (Fix f)) => Eq (Fix f) where
+  Fix a == Fix b = a == b
+
+instance Ord (f (Fix f)) => Ord (Fix f) where
+  Fix a `compare` Fix b = a `compare` b
+
+data Foo i r = Foo i r
+  deriving (Eq, Ord)
+
+newtype Bar a = Bar (M.Map Char (M.Map (Fix (Foo ())) Word))
+
+foo :: Bar a -> Bar a -> Bar a
+foo (Bar a) (Bar b) = Bar (M.unionWith M.union a b)