1 files changed, 2 insertions, 1 deletions
diff --git a/src/Data/Array/Nested/Types.hs b/src/Data/Array/Nested/Types.hs
index 4172fa0..b8a9aea 100644
--- a/src/Data/Array/Nested/Types.hs
+++ b/src/Data/Array/Nested/Types.hs
@@ -7,6 +7,7 @@
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeFamilyDependencies #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE ViewPatterns #-}
@@ -111,7 +112,7 @@ type family Replicate n a where
 lemReplicateSucc :: (a : Replicate n a) :~: Replicate (n + 1) a
 lemReplicateSucc = unsafeCoerceRefl
 
-type family MapJust l where
+type family MapJust l = r | r -> l where
   MapJust '[] = '[]
   MapJust (x : xs) = Just x : MapJust xs