diff --git a/Data/Boolean.hs b/Data/Boolean.hs
--- a/Data/Boolean.hs
+++ b/Data/Boolean.hs
@@ -25,6 +25,8 @@
 
   ) where
 
+import Data.List ( nub )
+
 -- | Boolean formulas are represented as values of type @Boolean@.
 -- 
 data Boolean
@@ -76,7 +78,7 @@
 -- 
 booleanToCNF :: Boolean -> CNF
 booleanToCNF
-  = map (map literal . disjunction)
+  = map (nub . map literal . disjunction)
   . conjunction
   . asLongAsPossible distribute
   . asLongAsPossible pushNots
diff --git a/incremental-sat-solver.cabal b/incremental-sat-solver.cabal
--- a/incremental-sat-solver.cabal
+++ b/incremental-sat-solver.cabal
@@ -1,5 +1,5 @@
 Name:          incremental-sat-solver
-Version:       0.1.3
+Version:       0.1.4
 Cabal-Version: >= 1.6
 Synopsis:      Simple, Incremental SAT Solving as a Library
 Description:   This Haskell library provides an implementation of the