diff --git a/phpBB/docs/CHANGELOG.html b/phpBB/docs/CHANGELOG.html
index 3441cc2c47..9789d8f2fe 100644
--- a/phpBB/docs/CHANGELOG.html
+++ b/phpBB/docs/CHANGELOG.html
@@ -118,6 +118,7 @@
 		<li>[Fix] Better thumbnail quality with imagemagick. (Bug #42565)</li>
 		<li>[Fix] Fix download count increments for image attachments without corresponding thumbnails. (Bug #42505)</li>
 		<li>[Fix] Fix wrong bot ip check if bot ip was wrongly entered by admin. (Bug #42485)</li>
+		<li>[Fix] Fix javascript errors in simple header (prosilver) by adding forum_fn.js and the corresponding variables. (Bug #42135)</li>
 		<li>[Change] Allow download of conflicting file for later reference in automatic updater</li>
 		<li>[Change] Default difference view is now 'inline' instead of 'side by side'</li>
 		<li>[Change] Added new option for merging differences to conflicting files in automatic updater</li>
diff --git a/phpBB/styles/prosilver/template/simple_header.html b/phpBB/styles/prosilver/template/simple_header.html
index d14f89935e..0e2409586c 100644
--- a/phpBB/styles/prosilver/template/simple_header.html
+++ b/phpBB/styles/prosilver/template/simple_header.html
@@ -17,6 +17,11 @@
 <script type="text/javascript">
 // <![CDATA[
 
+	var jump_page = '{LA_JUMP_PAGE}:';
+	var on_page = '{ON_PAGE}';
+	var per_page = '{PER_PAGE}';
+	var base_url = '{A_BASE_URL}';
+	var style_cookie = 'phpBBstyle';
 	var onload_functions = new Array();
 	var onunload_functions = new Array();
 	var style_cookie_settings = '{A_COOKIE_SETTINGS}';
@@ -43,6 +48,7 @@
 // ]]>
 </script>
 <script type="text/javascript" src="{T_TEMPLATE_PATH}/styleswitcher.js"></script>
+<script type="text/javascript" src="{T_TEMPLATE_PATH}/forum_fn.js"></script>
 
 <link href="{T_THEME_PATH}/print.css" rel="stylesheet" type="text/css" media="print" title="printonly" />
 <link href="{T_STYLESHEET_LINK}" rel="stylesheet" type="text/css" media="screen, projection" />