diff --git a/src/IDF/Template.php b/src/IDF/Template.php
new file mode 100644
index 0000000..b7b2668
--- /dev/null
+++ b/src/IDF/Template.php
@@ -0,0 +1,51 @@
+<?php
+/* -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+# ***** BEGIN LICENSE BLOCK *****
+# This file is part of InDefero, an open source project management application.
+# Copyright (C) 2011 Céondo Ltd and contributors.
+#
+# InDefero is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# InDefero is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#
+# ***** END LICENSE BLOCK ***** */
+
+/**
+ * PHP sets the backtrack limit quite low, so some (harder to analyze) regexes may fail
+ * unexpectedly on large inputs or weird cornercases (see issue 618). Unfortunately this
+ * fix does not always work and the execution time gets bigger the bigger we set the limit,
+ * so in case PCRE fails to analyze the input string and preg_replace(_callback) returns NULL,
+ * we at least return the input string unaltered.
+ *
+ * @param $pattern  The pattern
+ * @param $mixed    Callback or replacement string
+ * @param $input    The input
+ * @return The output
+ */
+function IDF_Template_safePregReplace($pattern, $mixed, $input)
+{
+    $pcre_backtrack_limit = ini_get('pcre.backtrack_limit');
+    ini_set('pcre.backtrack_limit', 10000000);
+   
+    if (is_string($mixed) && !function_exists($mixed))
+        $output = preg_replace($pattern, $mixed, $input);
+    else
+        $output = preg_replace_callback($pattern, $mixed, $input);
+
+    if ($output === null)
+        $output = $input;
+
+    ini_set('pcre.backtrack_limit', $pcre_backtrack_limit);
+    return $output;
+}
diff --git a/src/IDF/Template/IssueComment.php b/src/IDF/Template/IssueComment.php
index a3f23e5..287a8b3 100644
--- a/src/IDF/Template/IssueComment.php
+++ b/src/IDF/Template/IssueComment.php
@@ -22,6 +22,7 @@
 # ***** END LICENSE BLOCK ***** */
 
 Pluf::loadFunction('Pluf_HTTP_URL_urlForView');
+Pluf::loadFunction('IDF_Template_safePregReplace');
 
 /**
  * Make the links to issues and commits.
@@ -34,36 +35,31 @@ class IDF_Template_IssueComment extends Pluf_Template_Tag
 
     function start($text, $request, $echo=true, $wordwrap=true, $esc=true, $autolink=true, $nl2br=false)
     {
-        // PHP sets the backtrack limit quite low, so some regexes may
-        // fail unexpectedly on large inputs or weird cornercases (see issue 618)
-        $pcre_backtrack_limit = ini_get('pcre.backtrack_limit');
-        ini_set('pcre.backtrack_limit', 10000000);
-
         $this->project = $request->project;
         $this->request = $request;
         $this->scm = IDF_Scm::get($request->project);
         if ($esc) $text = Pluf_esc($text);
         if ($autolink) {
-            $text = preg_replace('#([a-z]+://[^\s\(\)]+)#i',
-                                 '<a href="\1">\1</a>', $text);
+            $text = IDF_Template_safePregReplace('#([a-z]+://[^\s\(\)]+)#i',
+                                                 '<a href="\1">\1</a>', $text);
         }
         if ($request->rights['hasIssuesAccess']) {
-            $text = preg_replace_callback('#((?:issue|bug|ticket)(s)?\s+|\s+\#)(\d+)(\#ic\d+)?(?(2)((?:[, \w]+(?:\s+\#)?)?\d+(?:\#ic\d+)?){0,})#im',
-                                          array($this, 'callbackIssues'), $text);
+            $text = IDF_Template_safePregReplace('#((?:issue|bug|ticket)(s)?\s+|\s+\#)(\d+)(\#ic\d+)?(?(2)((?:[, \w]+(?:\s+\#)?)?\d+(?:\#ic\d+)?){0,})#im',
+                                                 array($this, 'callbackIssues'), $text);
         }
         if ($request->rights['hasReviewAccess']) {
-            $text = preg_replace_callback('#(reviews?\s+)(\d+(?:(?:\s+and|\s+or|,)\s+\d+)*)\b#i',
-                                          array($this, 'callbackReviews'), $text);
+            $text = IDF_Template_safePregReplace('#(reviews?\s+)(\d+(?:(?:\s+and|\s+or|,)\s+\d+)*)\b#i',
+                                                 array($this, 'callbackReviews'), $text);
         }
         if ($request->rights['hasSourceAccess']) {
             $verbs = array('added', 'fixed', 'reverted', 'changed', 'removed');
             $nouns = array('commit', 'commits', 'revision', 'revisions', 'rev', 'revs');
             $prefix = implode(' in|', $verbs).' in' . '|'.
                       implode('|', $nouns);
-            $text = preg_replace_callback('#((?:'.$prefix.')(?:\s+r?))([0-9a-f]{1,40}((?:\s+and|\s+or|,)\s+r?[0-9a-f]{1,40})*)\b#i',
-                                          array($this, 'callbackCommits'), $text);
-            $text = preg_replace_callback('=(src:)([^\s@#,\(\)\\\\]+(?:(\\\\)[\s@#][^\s@#,\(\)\\\\]+){0,})+(?:\@([^\s#,]+))(?:#(\d+))?=im',
-                                          array($this, 'callbackSource'), $text);
+            $text = IDF_Template_safePregReplace('#((?:'.$prefix.')(?:\s+r?))([0-9a-f]{1,40}((?:\s+and|\s+or|,)\s+r?[0-9a-f]{1,40})*)\b#i',
+                                                 array($this, 'callbackCommits'), $text);
+            $text = IDF_Template_safePregReplace('=(src:)([^\s@#,\(\)\\\\]+(?:(\\\\)[\s@#][^\s@#,\(\)\\\\]+){0,})+(?:\@([^\s#,]+))(?:#(\d+))?=im',
+                                                 array($this, 'callbackSource'), $text);
         }
         if ($wordwrap) $text = Pluf_Text::wrapHtml($text, 69, "\n");
         if ($nl2br) $text = nl2br($text);
@@ -72,8 +68,6 @@ class IDF_Template_IssueComment extends Pluf_Template_Tag
         } else {
             return $text;
         }
-
-        ini_set('pcre.backtrack_limit', $pcre_backtrack_limit);
     }
 
     /**
@@ -101,9 +95,9 @@ class IDF_Template_IssueComment extends Pluf_Template_Tag
             }
             return $m[0]; // not existing issue.
         }
-        return preg_replace_callback('#(\#)?(\d+)(\#ic\d+)?#',
-                                     array($this, 'callbackIssue'),
-                                     $m[0]);
+        return IDF_Template_safePregReplace('#(\#)?(\d+)(\#ic\d+)?#',
+                                            array($this, 'callbackIssue'),
+                                            $m[0]);
     }
 
     /**
@@ -138,7 +132,7 @@ class IDF_Template_IssueComment extends Pluf_Template_Tag
             return $m[1].call_user_func(array($this, 'callbackCommit'), array($m[2]));
         }
         // Multiple commits like 'commits 6e030e6, a25bfc1 and 3c094f8'.
-        return $m[1].preg_replace_callback('#\b[0-9a-f]{1,40}\b#i', array($this, 'callbackCommit'), $m[2]);
+        return $m[1].IDF_Template_safePregReplace('#\b[0-9a-f]{1,40}\b#i', array($this, 'callbackCommit'), $m[2]);
     }
 
     /**
@@ -170,7 +164,7 @@ class IDF_Template_IssueComment extends Pluf_Template_Tag
     {
         $keyword = rtrim($m[1]);
         if ('reviews' === $keyword) {
-            return $m[1].preg_replace_callback('#\b(\d+)\b#i', array($this, 'callbackReview'), $m[2]);
+            return $m[1].IDF_Template_safePregReplace('#\b(\d+)\b#i', array($this, 'callbackReview'), $m[2]);
         } else if ('review' === $keyword) {
             return $m[1].call_user_func(array($this, 'callbackReview'), array('', $m[2]));
         }
diff --git a/src/IDF/Template/Markdown.php b/src/IDF/Template/Markdown.php
index 9b33a06..2652719 100644
--- a/src/IDF/Template/Markdown.php
+++ b/src/IDF/Template/Markdown.php
@@ -22,6 +22,7 @@
 # ***** END LICENSE BLOCK ***** */
 
 Pluf::loadFunction('Pluf_Text_MarkDown_parse');
+Pluf::loadFunction('IDF_Template_safePregReplace');
 
 /**
  * Make the links to issues and commits.
@@ -34,11 +35,6 @@ class IDF_Template_Markdown extends Pluf_Template_Tag
 
     function start($text, $request)
     {
-        // PHP sets the backtrack limit quite low, so some regexes may
-        // fail unexpectedly on large inputs or weird cornercases (see issue 618)
-        $pcre_backtrack_limit = ini_get('pcre.backtrack_limit');
-        ini_set('pcre.backtrack_limit', 10000000);
-
         $this->project = $request->project;
         $this->request = $request;
         // Replace like in the issue text
@@ -47,22 +43,20 @@ class IDF_Template_Markdown extends Pluf_Template_Tag
         // Replace [[[path/to/file.mdtext, commit]]] with embedding
         // the content of the file into the wki page
         if ($this->request->rights['hasSourceAccess']) {
-            $text = preg_replace_callback('#\[\[\[([^\,]+)(?:, ([^/]+))?\]\]\]#im',
-                                          array($this, 'callbackEmbeddedDoc'),
-                                          $text);
+            $text = IDF_Template_safePregReplace('#\[\[\[([^\,]+)(?:, ([^/]+))?\]\]\]#im',
+                                                 array($this, 'callbackEmbeddedDoc'),
+                                                 $text);
         }
         // Replace [Page]([[PageName]]) with corresponding link to the page, with link text being Page.
-        $text = preg_replace_callback('#\[([^\]]+)\]\(\[\[([A-Za-z0-9\-]+)\]\]\)#im',
-                                      array($this, 'callbackWikiPage'),
-                                      $text);
+        $text = IDF_Template_safePregReplace('#\[([^\]]+)\]\(\[\[([A-Za-z0-9\-]+)\]\]\)#im',
+                                             array($this, 'callbackWikiPage'),
+                                             $text);
         // Replace [[PageName]] with corresponding link to the page.
-        $text = preg_replace_callback('#\[\[([A-Za-z0-9\-]+)\]\]#im',
-                                      array($this, 'callbackWikiPageNoName'),
-                                      $text);
+        $text = IDF_Template_safePregReplace('#\[\[([A-Za-z0-9\-]+)\]\]#im',
+					     array($this, 'callbackWikiPageNoName'),
+					     $text);
         $filter = new IDF_Template_MarkdownPrefilter();
         echo $filter->go(Pluf_Text_MarkDown_parse($text));
-
-        ini_set('pcre.backtrack_limit', $pcre_backtrack_limit);
     }
 
     function callbackWikiPageNoName($m)