diff --git a/src/Data/Constraint/Trivial.hs b/src/Data/Constraint/Trivial.hs
--- a/src/Data/Constraint/Trivial.hs
+++ b/src/Data/Constraint/Trivial.hs
@@ -5,8 +5,9 @@
 -- Maintainer  :  (@) sagemuej $ smail.uni-koeln.de
 -- 
 {-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE ConstraintKinds   #-}
 
-module Data.Constraint.Trivial where
+module Data.Constraint.Trivial (Unconstrained, Impossible) where
 
 -- | Intended to be used as an argument for some type constructor which expects kind
 --   @* -> Constraint@, when you do not actually wish to constrain anything with it.
@@ -15,3 +16,12 @@
 --   changing anything.
 class Unconstrained t
 instance Unconstrained t
+
+
+-- | This constraint can /never/ be fulfilled. Might be useful e.g. as a default
+--   for a class-associated constraint; this basically disables any method with
+--   that constraint (so it can safely be left 'undefined').
+type Impossible t = HiddenEmptyClass t
+
+class HiddenEmptyClass t
+
diff --git a/trivial-constraint.cabal b/trivial-constraint.cabal
--- a/trivial-constraint.cabal
+++ b/trivial-constraint.cabal
@@ -2,8 +2,8 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                trivial-constraint
-version:             0.2.0.0
-synopsis:            A class / constraint that any type fulfills
+version:             0.3.0.0
+synopsis:            Constraints that any type, resp. no type fulfills
 description:         Since GHC 7.4, constraints are first-class: we have the constraint kind, and thus type-classes have a kind such as @* -> Constraint@.
                      .
                      These can be used as parameters to data types. They also can be combined quite nicely,
@@ -15,6 +15,7 @@
                      however you always need to start with a plain old type class when building constraints.
                      .
                      This library provides a type class that is not really a constraint at all, so you can "start from zero" with building up a custom constraint.
+                     Also its opposite (a constraint that no type can ever fulfill).
 license:             GPL-3
 license-file:        LICENSE
 author:              Justus Sagemüller
@@ -30,6 +31,6 @@
   exposed-modules:     Data.Constraint.Trivial
   -- other-modules:       
   -- other-extensions:    
-  build-depends:       base>=4 && <5
+  build-depends:       base>=4.5 && <5
   hs-source-dirs:      src
   default-language:    Haskell2010