diff --git a/one-liner.cabal b/one-liner.cabal
--- a/one-liner.cabal
+++ b/one-liner.cabal
@@ -1,5 +1,5 @@
 Name:                 one-liner
-Version:              0.2.1
+Version:              0.2.2
 Synopsis:             Constraint-based generics
 Description:          Write short and concise generic instances of type classes.
 Homepage:             https://github.com/sjoerdvisscher/one-liner
@@ -27,7 +27,7 @@
   
   Build-depends:
       base         >= 4.5 && < 5 
-    , transformers >= 0.3 && < 0.4
+    , transformers >= 0.3 && < 0.5
     , ghc-prim
 
 source-repository head
diff --git a/src/Generics/OneLiner/ADT.hs b/src/Generics/OneLiner/ADT.hs
--- a/src/Generics/OneLiner/ADT.hs
+++ b/src/Generics/OneLiner/ADT.hs
@@ -109,7 +109,7 @@
 
   -- | The constraints needed to run `buildsA` and `buildsRecA`. 
   -- It should be a list of all the types of the subcomponents of @t@, each applied to @c@.
-  type Constraints t c :: Constraint
+  type Constraints t (c :: * -> Constraint) :: Constraint
   
   buildsA :: (Constraints t c, Applicative f)
           => For c -- ^ Witness for the constraint @c@.
@@ -137,6 +137,8 @@
              -- result of applicatively applying the constructor to the results of the given function 
              -- for each field of the constructor.
   buildsRecA for sub _ = buildsA for sub
+  
+  {-# MINIMAL ctorIndex, (buildsA | buildsRecA) #-}
 
 -- | Add an instance for this class if the data type has exactly one constructor.
 --
@@ -187,6 +189,7 @@
 
 
 
+
 infixl 9 !
 -- | Get the subcomponent by using the projector from the field information.
 (!) :: t -> FieldInfo (t -> s) -> s
@@ -259,7 +262,7 @@
     [ Left  <$> f (FieldInfo (\(Left a)  -> a))
     , Right <$> f (FieldInfo (\(Right a) -> a))
     ]
-
+    
 instance ADT (Maybe a) where
 
   ctorIndex Nothing = 0
diff --git a/src/Generics/OneLiner/ADT1.hs b/src/Generics/OneLiner/ADT1.hs
--- a/src/Generics/OneLiner/ADT1.hs
+++ b/src/Generics/OneLiner/ADT1.hs
@@ -104,7 +104,7 @@
 
   -- | The constraints needed to run `buildsA` and `buildsRecA`. 
   -- It should be a list of all the types of the subcomponents of @t@, each applied to @c@.
-  type Constraints t c :: Constraint
+  type Constraints t (c :: (* -> *) -> Constraint) :: Constraint
   buildsA :: (Constraints t c, Applicative f)
           => For c -- ^ Witness for the constraint @c@.
           -> (FieldInfo (Extract t) -> f b)
@@ -125,6 +125,8 @@
              -> (FieldInfo (t :~> t) -> f (t b))
              -> [f (t b)]
   buildsRecA for param sub _ = buildsA for param sub
+  
+  {-# MINIMAL ctorIndex, (buildsA | buildsRecA) #-}
 
 -- | Add an instance for this class if the data type has exactly one constructor.
 --