diff --git a/README.md b/README.md
index 5f1d0ec..d6e8443 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ fast_align
 `fast_align` is a simple, fast, unsupervised word aligner.
 
 If you use this software, please cite:
-* [Chris Dyer](http://www.cs.cmu.edu/~cdyer), [Victor Chahuneau](http://victor.chahuneau.fr), and [Noah A. Smith](http://www.cs.cmu.edu/~nasmith). (2013). [A Simple, Fast, and Effective Reparameterization of IBM Model 2](http://www.ark.cs.cmu.edu/cdyer/fast_valign.pdf). In *Proc. of NAACL*.
+* [Chris Dyer](http://www.cs.cmu.edu/~cdyer), [Victor Chahuneau](http://victor.chahuneau.fr), and [Noah A. Smith](http://www.cs.cmu.edu/~nasmith). (2013). [A Simple, Fast, and Effective Reparameterization of IBM Model 2](http://www.aclweb.org/anthology/N13-1073). In *Proc. of NAACL*.
 
 The source code in this repository is provided under the terms of the [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0.html).
 
diff --git a/src/da.h b/src/da.h
index 80f7529..bfc6c45 100644
--- a/src/da.h
+++ b/src/da.h
@@ -86,7 +86,7 @@ struct DiagonalAlignment {
     const double x_1 = a_1 * g_1;
     const double g_2 = g_1 * r;
     const double rm1 = r - 1;
-    return (a_n * g_np1 - x_1) / rm1 - d*(g_np1 - g_2) / (rm1 * rm1);
+    return (a_n * g_np1 - x_1) / rm1 + d*(g_np1 - g_2) / (rm1 * rm1);
   }
 };