diff --git a/INSTALL b/INSTALL
index 78be45b54..eaee99b6d 100644
--- a/INSTALL
+++ b/INSTALL
@@ -12,7 +12,7 @@ REQUIREMENTS
 * An IMAP, HTTP and SMTP server
 * .htaccess support allowing overrides for DirectoryIndex
 * PHP Version 5.4 or greater including:
-   - PCRE, DOM, JSON, Session, Sockets, OpenSSL, Mbstring, Ctype (required)
+   - PCRE, DOM, JSON, Session, Sockets, OpenSSL, Mbstring, Filter, Ctype (required)
    - PHP PDO with driver for either MySQL, PostgreSQL, SQL Server, Oracle or SQLite (required)
    - Iconv, Zip, Fileinfo, Intl, Exif (recommended)
    - LDAP for LDAP addressbook support (optional)
diff --git a/installer/check.php b/installer/check.php
index 2500e8cba..e1fa76297 100644
--- a/installer/check.php
+++ b/installer/check.php
@@ -31,6 +31,7 @@ $required_php_exts = array(
     'PDO'       => 'PDO',
     'Multibyte' => 'mbstring',
     'OpenSSL'   => 'openssl',
+    'Filter'    => 'filter',
     'Ctype'     => 'ctype',
 );
 
@@ -88,6 +89,7 @@ $source_urls = array(
     'GD'        => 'http://www.php.net/manual/en/book.image.php',
     'Imagick'   => 'http://www.php.net/manual/en/book.imagick.php',
     'Zip'       => 'http://www.php.net/manual/en/book.zip.php',
+    'Filter'    => 'http://www.php.net/manual/en/book.filter.php',
     'Ctype'     => 'http://www.php.net/manual/en/book.ctype.php',
     'pdo_mysql'   => 'http://www.php.net/manual/en/ref.pdo-mysql.php',
     'pdo_pgsql'   => 'http://www.php.net/manual/en/ref.pdo-pgsql.php',
diff --git a/program/lib/Roundcube/README.md b/program/lib/Roundcube/README.md
index 2c242b025..d796d480b 100644
--- a/program/lib/Roundcube/README.md
+++ b/program/lib/Roundcube/README.md
@@ -19,7 +19,7 @@ tasks:
 REQUIREMENTS
 ------------
 PHP Version 5.4 or greater including:
-   - PCRE, DOM, JSON, Session, Sockets, OpenSSL, Mbstring, Ctype (required)
+   - PCRE, DOM, JSON, Session, Sockets, OpenSSL, Mbstring, Filter, Ctype (required)
    - PHP PDO with driver for either MySQL, PostgreSQL, SQL Server, Oracle or SQLite (required)
    - Libiconv, Zip, Fileinfo, Intl, Exif (recommended)
    - LDAP for LDAP addressbook support (optional)