1 files changed, 16 insertions, 0 deletions
diff --git a/testsuite/tests/gadt/T3169.hs b/testsuite/tests/gadt/T3169.hs
new file mode 100644
index 0000000000..b52ec2cf87
--- /dev/null
+++ b/testsuite/tests/gadt/T3169.hs
@@ -0,0 +1,16 @@
+{-# LANGUAGE  TypeFamilies, ScopedTypeVariables #-}
+module T3169 where
+
+import Prelude hiding ( lookup )
+
+class Key k where
+  type Map k :: * -> *
+  lookup :: k -> Map k elt -> Maybe elt
+
+instance (Key a, Key b) => Key (a,b) where
+  type Map (a,b) = MP a b
+  lookup (a,b) (m :: Map (a,b) elt) 
+     = case lookup a m :: Maybe (Map b elt) of
+	  Just (m2 :: Map b elt) -> lookup b m2 :: Maybe elt
+
+data MP a b elt = MP (Map a (Map b elt))