It's bison 2.5 that's actually required now.

README.md

@@ -52,7 +52,7 @@ A number of tools and libraries are needed in order to recompile everything. You
 - [MATLAB](http://www.dynare.org/DynareWiki/BuildingDynareFromSource?action=AttachFile&do=view&target=dynare-mingw64-libs.zip) (if you want to compile MEX for MATLAB)
 - [GNU Octave](http://www.octave.org), with the development headers (if you want to compile MEX for Octave)
 - [Boost libraries](http://www.boost.org), version 1.36 or later
-- [Bison](http://www.gnu.org/software/bison/), version 2.4 or later (only if you get the source through Git)
+- [Bison](http://www.gnu.org/software/bison/), version 2.5 or later (only if you get the source through Git)
 - [Flex](http://flex.sourceforge.net/), version 2.5.4 or later (only if you get the source through Git)
 - [Autoconf](http://www.gnu.org/software/autoconf/), version 2.62 or later (only if you get the source through Git) (see [Installing an updated version of Autoconf in your own directory, in GNU/Linux](http://www.dynare.org/DynareWiki/AutoMake))
 - [Automake](http://www.gnu.org/software/automake/), version 1.11.2 or later (only if you get the source through Git) (see [Installing an updated version of AutoMake in your own directory, in GNU/Linux](http://www.dynare.org/DynareWiki/AutoMake))

preprocessor/DynareBison.yy

 /*
- * Copyright (C) 2003-2013 Dynare Team
+ * Copyright (C) 2003-2014 Dynare Team
  *
  * This file is part of Dynare.
  *
@@ -18,7 +18,7 @@
  */
 
 %skeleton "lalr1.cc"
-%require "2.4"
+%require "2.5"
 %defines
 
 %code top {

preprocessor/macro/MacroBison.yy

 /*
- * Copyright (C) 2008-2013 Dynare Team
+ * Copyright (C) 2008-2014 Dynare Team
  *
  * This file is part of Dynare.
  *
@@ -18,7 +18,7 @@
  */
 
 %skeleton "lalr1.cc"
-%require "2.4"
+%require "2.5"
 %defines
 
 %code top {