1 files changed, 27 insertions, 0 deletions
diff --git a/testsuite/tests/gadt/T2040.hs b/testsuite/tests/gadt/T2040.hs
new file mode 100644
index 0000000000..2ff4777523
--- /dev/null
+++ b/testsuite/tests/gadt/T2040.hs
@@ -0,0 +1,27 @@
+{-# LANGUAGE GADTs, ScopedTypeVariables, FlexibleContexts,
+             MultiParamTypeClasses #-}
+{-# OPTIONS_GHC -Wall #-}
+
+module T2040 where
+
+data Teq a b where Teq :: Teq a a
+
+class C a b where proof :: Teq a b
+
+data S a = S a
+
+data W b where
+    -- This would make every version of GHC happy
+    -- W :: (C a c , c ~ S b) => W a -> W c
+    W :: C a (S b) => W a -> W (S b)
+
+foo :: W (S ()) -> W (S ()) -> ()
+foo (W (_ :: W a1)) (W (_ :: W a2)) =
+  case proof :: Teq a1 (S ()) of
+    Teq -> ()
+
+foo2 :: W (S ()) -> W (S ()) -> ()
+foo2 (W (_ :: W a1)) (W (_ :: W a2)) =
+  case proof :: Teq a1 (S ()) of
+    Teq -> case proof :: Teq a2 (S ()) of
+             Teq ->  ()
+\ No newline at end of file