diff --git a/CHANGES.txt b/CHANGES.txt
index f2362b8..f4f9efb 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,3 +1,9 @@
+Version 3.13.1 (11/03/2022)
+--------------
+- Fixed deprecation warning messages displayed by PHP 8.1.
+- Fixed problem with file encoding of Text class.
+- Improved accuracy of HSL to RGB conversion.
+
 Version 3.13 (14/02/2022)
 ------------
 - Added curved line graph support with line_curve option.
diff --git a/README.txt b/README.txt
index a8db88d..9bb1243 100644
--- a/README.txt
+++ b/README.txt
@@ -1,5 +1,5 @@
-SVGGraph Library version 3.13
-=============================
+SVGGraph Library version 3.13.1
+===============================
 
 This library provides PHP classes and functions for easily creating SVG
 graphs from data. Version 3.0 of SVGGraph requires at least PHP 5.4 - if
diff --git a/SVGGraph.php b/SVGGraph.php
index 6dec2e6..d465a09 100644
--- a/SVGGraph.php
+++ b/SVGGraph.php
@@ -25,7 +25,7 @@ class SVGGraph {
 
   use SVGGraphTrait;
 
-  const VERSION = 'SVGGraph 3.13';
+  const VERSION = 'SVGGraph 3.13.1';
   private $width = 100;
   private $height = 100;
   private $settings = [];
diff --git a/StackedCylinderGraph.php b/StackedCylinderGraph.php
index a1ea196..8df08e5 100644
--- a/StackedCylinderGraph.php
+++ b/StackedCylinderGraph.php
@@ -1,6 +1,6 @@
 <?php
 /**
- * Copyright (C) 2013-2019 Graham Breach
+ * Copyright (C) 2013-2022 Graham Breach
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Lesser General Public License as published by