diff --git a/aclocal/ac_prog_bison.m4 b/aclocal/ac_prog_bison.m4
index 1e2d200..c74b4f1 100644
--- a/aclocal/ac_prog_bison.m4
+++ b/aclocal/ac_prog_bison.m4
@@ -1,6 +1,6 @@
 dnl
 dnl Check Bison version
-dnl AC_PROG_BISON([MIN_VERSION=2.6])
+dnl AC_PROG_BISON([MIN_VERSION=2.4])
 dnl
 dnl Will define BISON_USE_PARSER_H_EXTENSION if Automake is < 1.11
 dnl for use with .h includes.
@@ -8,7 +8,7 @@
 
 AC_DEFUN([AC_PROG_BISON], [
 if test "x$1" = "x" ; then
-  bison_required_version="2.6"
+  bison_required_version="2.4"
 else
   bison_required_version="$1"
 fi
@@ -27,7 +27,7 @@
   if test "$bison_version" \< "$bison_required_version" ; then
     BISON=:
     AC_MSG_RESULT([no])
-    AC_MSG_ERROR([Bison version 2.6 or higher must be installed on the system!])
+    AC_MSG_ERROR([Bison version 2.4 or higher must be installed on the system!])
   else
     AC_MSG_RESULT([yes])
     BISON=bison