diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-[![Build Status](https://travis-ci.org/arowM/haskell-bookkeeping.svg?branch=master)](https://travis-ci.org/arowM/heterocephalus)
+[![Build Status](https://travis-ci.org/arowM/haskell-bookkeeping.svg?branch=master)](https://travis-ci.org/arowM/haskell-bookkeeping)
 [![Hackage](https://img.shields.io/hackage/v/bookkeeping.svg)](https://hackage.haskell.org/package/bookkeeping)
 [![Stackage LTS](http://stackage.org/package/bookkeeping/badge/lts)](http://stackage.org/lts/package/bookkeeping)
 [![Stackage Nightly](http://stackage.org/package/bookkeeping/badge/nightly)](http://stackage.org/nightly/package/bookkeeping)
diff --git a/bookkeeping.cabal b/bookkeeping.cabal
--- a/bookkeeping.cabal
+++ b/bookkeeping.cabal
@@ -1,5 +1,5 @@
 name:                bookkeeping
-version:             0.2.0.1
+version:             0.2.1.0
 synopsis:            A module for bookkeeping by double entry.
 description:
     A module for bookkeeping by double entry. This module provides a way to do bookkeeping programmatically.
diff --git a/src/Business/Bookkeeping.hs b/src/Business/Bookkeeping.hs
--- a/src/Business/Bookkeeping.hs
+++ b/src/Business/Bookkeeping.hs
@@ -201,15 +201,15 @@
 
 newtype Year = Year
   { unYear :: Integer
-  } deriving (Show, Read, Ord, Eq, Num)
+  } deriving (Show, Read, Ord, Eq, Num, Enum)
 
 newtype Month = Month
   { unMonth :: Int
-  } deriving (Show, Read, Ord, Eq, Num)
+  } deriving (Show, Read, Ord, Eq, Num, Enum)
 
 newtype Date = Date
   { unDate :: Int
-  } deriving (Show, Read, Ord, Eq, Num)
+  } deriving (Show, Read, Ord, Eq, Num, Enum)
 
 newtype Description = Description
   { unDescription :: Text