1 files changed, 20 insertions, 0 deletions
diff --git a/testsuite/tests/indexed-types/should_fail/T2627b.hs b/testsuite/tests/indexed-types/should_fail/T2627b.hs
new file mode 100644
index 0000000000..13dbd9cb26
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_fail/T2627b.hs
@@ -0,0 +1,20 @@
+{-# LANGUAGE GADTs, TypeFamilies, EmptyDataDecls #-}
+
+module T2627b where
+
+data R a b
+data W a b
+data Z
+
+type family Dual a
+type instance Dual Z = Z
+type instance Dual (R a b) = W a (Dual b)
+type instance Dual (W a b) = R a (Dual b)
+
+data Comm a where
+    Rd :: (a -> Comm b) -> Comm (R a b)
+    Wr :: a  -> Comm b  -> Comm (W a b)
+    Fin :: Int -> Comm Z
+
+conn :: (Dual a ~ b, Dual b ~ a) => Comm a -> Comm b -> (Int, Int)
+conn (Rd k) (Wr a r) = conn undefined undefined