diff --git a/prolog-graph-lib.cabal b/prolog-graph-lib.cabal
--- a/prolog-graph-lib.cabal
+++ b/prolog-graph-lib.cabal
@@ -1,5 +1,5 @@
 Name:                prolog-graph-lib
-Version:             0.2.1
+Version:             0.2.1.1
 Synopsis:            Generating images of resolution trees for Prolog queries.
 Description:         This is the library part (See <http://hackage.haskell.org/package/prolog-graph> for the command line tool).
 License:             PublicDomain
@@ -13,7 +13,7 @@
   Exposed-Modules: Language.Prolog.GraphViz
   Other-Modules: GraphViz
   Build-depends:
-    prolog >= 0.2.0.1,
+    prolog >= 0.2.1,
     base >=4 && <5,
     fgl >= 5.4.2.4,
     mtl >= 2.0.1.0,