diff --git a/CHANGELOG.md b/CHANGELOG.md
index a409682b2..916e18bb8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@
 - Added `m4a` extension support in M3U playback [\#1724](https://github.com/torrentpier/torrentpier/pull/1724) ([belomaxorka](https://github.com/belomaxorka))
 - Created `VersionHelper.php` [\#1731](https://github.com/torrentpier/torrentpier/pull/1731) ([belomaxorka](https://github.com/belomaxorka))
 - Drop Ocelot announcer support 🫡 [\#1727](https://github.com/torrentpier/torrentpier/pull/1727) ([belomaxorka](https://github.com/belomaxorka))
+- Use `DEFAULT_CHARSET` constant instead of hardcoded string [\#1734](https://github.com/torrentpier/torrentpier/pull/1734) ([belomaxorka](https://github.com/belomaxorka))
 - Replaced some `html_entity_decode` to engine's built-in function [\#1733](https://github.com/torrentpier/torrentpier/pull/1733) ([belomaxorka](https://github.com/belomaxorka))
 - Show torrent's announcers list in `filelist.php` page [\#1708](https://github.com/torrentpier/torrentpier/pull/1708) ([belomaxorka](https://github.com/belomaxorka))
 - [PHP 8.4] Fixed some deprecations [\#1718](https://github.com/torrentpier/torrentpier/pull/1718) ([belomaxorka](https://github.com/belomaxorka))
diff --git a/admin/index.php b/admin/index.php
index e91d7ef16..110544328 100644
--- a/admin/index.php
+++ b/admin/index.php
@@ -234,7 +234,7 @@ if (isset($_GET['pane']) && $_GET['pane'] == 'left') {
 } else {
     // Generate frameset
     $template->assign_vars([
-        'CONTENT_ENCODING' => $bb_cfg['charset'],
+        'CONTENT_ENCODING' => DEFAULT_CHARSET,
         'TPL_ADMIN_FRAMESET' => true,
     ]);
     send_no_cache_headers();
diff --git a/common.php b/common.php
index 9a11e06ff..eaf360c13 100644
--- a/common.php
+++ b/common.php
@@ -239,7 +239,7 @@ function clean_filename($fname)
  * @param ?string $charset
  * @return string
  */
-function htmlCHR($txt, bool $double_encode = false, int $quote_style = ENT_QUOTES, ?string $charset = 'UTF-8'): string
+function htmlCHR($txt, bool $double_encode = false, int $quote_style = ENT_QUOTES, ?string $charset = DEFAULT_CHARSET): string
 {
     return (string)htmlspecialchars($txt ?? '', $quote_style, $charset, $double_encode);
 }
diff --git a/dl.php b/dl.php
index ce37c5b80..5b8852a96 100644
--- a/dl.php
+++ b/dl.php
@@ -53,7 +53,7 @@ function send_file_to_browser($attachment, $upload_dir)
     header('Pragma: public');
     $real_filename = clean_filename(basename($attachment['real_filename']));
     $mimetype = $attachment['mimetype'] . ';';
-    $charset = "charset={$bb_cfg['charset']};";
+    $charset = 'charset=' . DEFAULT_CHARSET . ';';
 
     // Send out the Headers
     header("Content-Type: $mimetype $charset name=\"$real_filename\"");
diff --git a/info.php b/info.php
index 3a66fae2a..0a75bf23a 100644
--- a/info.php
+++ b/info.php
@@ -43,7 +43,7 @@ switch ((string)$_REQUEST['show'] ?? 'not_found') {
 $require = is_file($htmlDir . $info['src']) ? ($htmlDir . $info['src']) : false;
 
 $template->assign_vars([
-    'PAGE_TITLE' => mb_strtoupper($info['title'], 'UTF-8'),
+    'PAGE_TITLE' => mb_strtoupper($info['title'], DEFAULT_CHARSET),
     'REQUIRE' => $require ? file_get_contents($require) : $lang['NOT_FOUND'],
 ]);
 
diff --git a/library/ajax/ffprobe_info.php b/library/ajax/ffprobe_info.php
index eaf72e43c..31753d4d7 100644
--- a/library/ajax/ffprobe_info.php
+++ b/library/ajax/ffprobe_info.php
@@ -57,15 +57,15 @@ if (isset($ffpInfo->streams)) {
         $result = '<span class="warnColor2">' . sprintf($lang['AUDIO_TRACK'], (!isset($stream->index) || $stream->index === 0) ? 1 : $stream->index) . '</span><br/>';
         if (isset($stream->tags->language)) {
             if (isset($stream->tags->title)) {
-                $result .= '<b>' . mb_strtoupper($stream->tags->language, 'UTF-8') . ' (' . $stream->tags->title . ')' . '</b>';
+                $result .= '<b>' . mb_strtoupper($stream->tags->language, DEFAULT_CHARSET) . ' (' . $stream->tags->title . ')' . '</b>';
             } else {
-                $result .= '<b>' . mb_strtoupper($stream->tags->language, 'UTF-8') . '</b>';
+                $result .= '<b>' . mb_strtoupper($stream->tags->language, DEFAULT_CHARSET) . '</b>';
             }
             $result .= '<br/>';
         }
 
         if (!empty($stream->codec_name)) {
-            $result .= sprintf($lang['AUDIO_CODEC'], $stream->codec_long_name, mb_strtoupper($stream->codec_name, 'UTF-8')) . '<br/>';
+            $result .= sprintf($lang['AUDIO_CODEC'], $stream->codec_long_name, mb_strtoupper($stream->codec_name, DEFAULT_CHARSET)) . '<br/>';
         }
         if (!empty($stream->bit_rate)) {
             $result .= sprintf($lang['BITRATE'], humn_bitrate((int)$stream->bit_rate)) . '<br/>';
@@ -87,7 +87,7 @@ if (isset($ffpInfo->streams)) {
     $data = [
         'filesize' => sprintf($lang['FILESIZE'] . ': <b>%s</b>', humn_size($ffpInfo->format->size)),
         'resolution' => (!$isAudio && isset($videoCodecInfo)) ? sprintf($lang['RESOLUTION'], $videoCodecInfo->width . 'x' . $videoCodecInfo->height) : '',
-        'video_codec' => (!$isAudio && isset($videoCodecInfo->codec_name)) ? sprintf($lang['VIDEO_CODEC'], $videoCodecInfo->codec_long_name, mb_strtoupper($videoCodecInfo->codec_name, 'UTF-8')) : '',
+        'video_codec' => (!$isAudio && isset($videoCodecInfo->codec_name)) ? sprintf($lang['VIDEO_CODEC'], $videoCodecInfo->codec_long_name, mb_strtoupper($videoCodecInfo->codec_name, DEFAULT_CHARSET)) : '',
         'audio_dub' => implode('<hr/>', $audioDub)
     ];
 
diff --git a/library/ajax/posts.php b/library/ajax/posts.php
index 76a589bc3..5a3632da9 100644
--- a/library/ajax/posts.php
+++ b/library/ajax/posts.php
@@ -85,7 +85,7 @@ switch ($this->request['type']) {
         if ($post['post_id'] == $post['topic_first_post_id']) {
             $message = "[quote]" . $post['topic_title'] . "[/quote]\r";
         }
-        if (mb_strlen($message, 'UTF-8') > 1000) {
+        if (mb_strlen($message, DEFAULT_CHARSET) > 1000) {
             $this->response['redirect'] = make_url(POSTING_URL . '?mode=quote&' . POST_POST_URL . '=' . $post_id);
         }
 
@@ -112,7 +112,7 @@ switch ($this->request['type']) {
         if ($post['poster_id'] != $userdata['user_id'] && !$is_auth['auth_mod']) {
             $this->ajax_die($lang['EDIT_OWN_POSTS']);
         }
-        if ((mb_strlen($post['post_text'], 'UTF-8') > 1000) || $post['post_attachment'] || ($post['topic_first_post_id'] == $post_id)) {
+        if ((mb_strlen($post['post_text'], DEFAULT_CHARSET) > 1000) || $post['post_attachment'] || ($post['topic_first_post_id'] == $post_id)) {
             $this->response['redirect'] = make_url(POSTING_URL . '?mode=editpost&' . POST_POST_URL . '=' . $post_id);
         } elseif ($this->request['type'] == 'editor') {
             $text = (string)$this->request['text'];
diff --git a/library/config.php b/library/config.php
index 7c887c51d..b1d7f0bb8 100644
--- a/library/config.php
+++ b/library/config.php
@@ -170,7 +170,6 @@ $bb_cfg['posting_url'] = 'posting.php'; # "http://{$domain_name}/posting.php"
 $bb_cfg['pm_url'] = 'privmsg.php'; # "http://{$domain_name}/privmsg.php"
 
 // Language
-$bb_cfg['charset'] = 'UTF-8';
 $bb_cfg['lang'] = [
     // Languages available for selecting
     'af' => [
diff --git a/library/defines.php b/library/defines.php
index f087efa17..d3ce318a9 100644
--- a/library/defines.php
+++ b/library/defines.php
@@ -30,13 +30,16 @@ define('TEMPLATES_DIR', BB_PATH . '/styles/templates');
 
 // System
 define('APP_NAME', 'TorrentPier');
+define('DEFAULT_CHARSET', 'UTF-8');
 define('UPDATER_URL', 'https://api.github.com/repos/torrentpier/torrentpier/releases');
 define('UPDATER_FILE', INT_DATA_DIR . '/updater.json');
-define('API_IP_URL', 'https://freeipapi.com/api/json/');
 define('CHECKSUMS_FILE', INT_DATA_DIR . '/checksums.md5');
 define('RESTORE_CORRUPT_CONFIRM_FILE', INT_DATA_DIR . '/rescorrupt.integrity');
 define('COOKIE_DBG', 'bb_dbg');
 
+// TODO: Move in another section
+define('API_IP_URL', 'https://freeipapi.com/api/json/');
+
 // Templates
 define('ADMIN_TPL_DIR', TEMPLATES_DIR . '/admin/');
 define('XS_USE_ISSET', '1');
diff --git a/library/includes/functions.php b/library/includes/functions.php
index 9a2f8860d..2300e3141 100644
--- a/library/includes/functions.php
+++ b/library/includes/functions.php
@@ -772,13 +772,13 @@ function get_user_id($username)
 
 function str_short($text, $max_length, $space = ' ')
 {
-    if (!empty($max_length) && !empty($text) && (mb_strlen($text, 'UTF-8') > $max_length)) {
-        $text = mb_substr($text, 0, $max_length, 'UTF-8');
+    if (!empty($max_length) && !empty($text) && (mb_strlen($text, DEFAULT_CHARSET) > $max_length)) {
+        $text = mb_substr($text, 0, $max_length, DEFAULT_CHARSET);
 
         if ($last_space_pos = $max_length - (int)strpos(strrev($text), (string)$space)) {
             if ($last_space_pos > round($max_length * 3 / 4)) {
                 $last_space_pos--;
-                $text = mb_substr($text, 0, $last_space_pos, 'UTF-8');
+                $text = mb_substr($text, 0, $last_space_pos, DEFAULT_CHARSET);
             }
         }
         $text .= '...';
@@ -927,7 +927,7 @@ function bb_update_config($params, $table = BB_CONFIG)
 
 function clean_username($username)
 {
-    $username = mb_substr(htmlspecialchars(str_replace("\'", "'", trim($username))), 0, 25, 'UTF-8');
+    $username = mb_substr(htmlspecialchars(str_replace("\'", "'", trim($username))), 0, 25, DEFAULT_CHARSET);
     $username = rtrim($username, "\\");
     $username = str_replace("'", "\'", $username);
 
@@ -1372,7 +1372,7 @@ function bb_simple_die($txt, $status_code = null)
 {
     global $bb_cfg;
 
-    header('Content-Type: text/plain; charset=' . $bb_cfg['charset']);
+    header('Content-Type: text/plain; charset=' . DEFAULT_CHARSET);
 
     if (isset($status_code)) {
         http_response_code($status_code);
@@ -2028,9 +2028,9 @@ function hash_search($hash)
     $info_hash = DB()->escape(pack('H*', $hash));
 
     // Check info_hash version
-    if (mb_strlen($hash, 'UTF-8') == 40) {
+    if (mb_strlen($hash, DEFAULT_CHARSET) == 40) {
         $info_hash_where = "WHERE info_hash = '$info_hash'";
-    } elseif (mb_strlen($hash, 'UTF-8') == 64) {
+    } elseif (mb_strlen($hash, DEFAULT_CHARSET) == 64) {
         $info_hash_where = "WHERE info_hash_v2 = '$info_hash'";
     } else {
         bb_die(sprintf($lang['HASH_INVALID'], $hash));
diff --git a/library/includes/init_bb.php b/library/includes/init_bb.php
index a823ccecb..bf3b298bd 100644
--- a/library/includes/init_bb.php
+++ b/library/includes/init_bb.php
@@ -364,7 +364,7 @@ function commify(?float $num, int $decimals = 0, ?string $decimal_separator = '.
  * @param string $encoding
  * @return string
  */
-function html_ent_decode(string $string, int $flags = ENT_QUOTES, string $encoding = 'UTF-8'): string
+function html_ent_decode(string $string, int $flags = ENT_QUOTES, string $encoding = DEFAULT_CHARSET): string
 {
     return html_entity_decode($string, $flags, $encoding);
 }
diff --git a/library/includes/page_header.php b/library/includes/page_header.php
index c4b72c0e4..a4f0434e7 100644
--- a/library/includes/page_header.php
+++ b/library/includes/page_header.php
@@ -111,7 +111,7 @@ $template->assign_vars([
 // The following assigns all _common_ variables that may be used at any point in a template
 $template->assign_vars([
     'SIMPLE_HEADER' => !empty($gen_simple_header),
-    'CONTENT_ENCODING' => $bb_cfg['charset'],
+    'CONTENT_ENCODING' => DEFAULT_CHARSET,
 
     'IN_ADMIN' => defined('IN_ADMIN'),
     'USER_HIDE_CAT' => (BB_SCRIPT == 'index'),
diff --git a/library/includes/ucp/register.php b/library/includes/ucp/register.php
index f43f15c49..663497036 100644
--- a/library/includes/ucp/register.php
+++ b/library/includes/ucp/register.php
@@ -481,7 +481,7 @@ foreach ($profile_fields as $field => $can_edit) {
             if ($submit && $sig != $pr_data['user_sig']) {
                 $sig = prepare_message($sig);
 
-                if (mb_strlen($sig, 'UTF-8') > $bb_cfg['max_sig_chars']) {
+                if (mb_strlen($sig, DEFAULT_CHARSET) > $bb_cfg['max_sig_chars']) {
                     $errors[] = $lang['SIGNATURE_TOO_LONG'];
                 } elseif (preg_match('#<(a|b|i|u|table|tr|td|img) #i', $sig) || preg_match('#(href|src|target|title)=#i', $sig)) {
                     $errors[] = $lang['SIGNATURE_ERROR_HTML'];
diff --git a/src/Dev.php b/src/Dev.php
index ce990aaa0..08187f428 100644
--- a/src/Dev.php
+++ b/src/Dev.php
@@ -255,7 +255,7 @@ class Dev
         $sql = str_compact($sql);
 
         if (!empty($_COOKIE['sql_log_full'])) {
-            if (mb_strlen($sql, 'UTF-8') > $max_len) {
+            if (mb_strlen($sql, DEFAULT_CHARSET) > $max_len) {
                 $sql = mb_substr($sql, 0, 50) . ' [...cut...] ' . mb_substr($sql, -50);
             }
         }
diff --git a/src/Helpers/VersionHelper.php b/src/Helpers/VersionHelper.php
index 665342407..00767ac01 100644
--- a/src/Helpers/VersionHelper.php
+++ b/src/Helpers/VersionHelper.php
@@ -31,7 +31,7 @@ class VersionHelper
     public static function removerPrefix(string $version): string
     {
         $version = trim($version);
-        $version = mb_strtolower($version, 'UTF-8');
+        $version = mb_strtolower($version, DEFAULT_CHARSET);
         return str_replace(self::VERSION_PREFIX, '', $version);
     }
 
diff --git a/src/Legacy/BBCode.php b/src/Legacy/BBCode.php
index 98df22726..17c12ab6f 100644
--- a/src/Legacy/BBCode.php
+++ b/src/Legacy/BBCode.php
@@ -322,7 +322,7 @@ class BBCode
     {
         $max_len = 70;
         $href = $m[1];
-        $name = (mb_strlen($href, 'UTF-8') > $max_len) ? mb_substr($href, 0, $max_len - 19) . '...' . mb_substr($href, -16) : $href;
+        $name = (mb_strlen($href, DEFAULT_CHARSET) > $max_len) ? mb_substr($href, 0, $max_len - 19) . '...' . mb_substr($href, -16) : $href;
 
         return $this->nofollow_url($href, $name);
     }
diff --git a/src/Updater.php b/src/Updater.php
index 6eb4ab722..c4f8f0f00 100644
--- a/src/Updater.php
+++ b/src/Updater.php
@@ -62,7 +62,7 @@ class Updater
         $response = file_get_contents(UPDATER_URL, context: $context);
 
         if ($response !== false) {
-            $this->jsonResponse = json_decode(mb_convert_encoding($response, 'UTF-8', mb_detect_encoding($response)), true);
+            $this->jsonResponse = json_decode(mb_convert_encoding($response, DEFAULT_CHARSET, mb_detect_encoding($response)), true);
         }
 
         // Empty JSON result
diff --git a/src/Validate.php b/src/Validate.php
index 95c742376..7f4e03380 100644
--- a/src/Validate.php
+++ b/src/Validate.php
@@ -45,10 +45,10 @@ class Validate
         $username = clean_username($username);
 
         // Length
-        if (mb_strlen($username, 'UTF-8') > USERNAME_MAX_LENGTH) {
+        if (mb_strlen($username, DEFAULT_CHARSET) > USERNAME_MAX_LENGTH) {
             return $lang['USERNAME_TOO_LONG'];
         }
-        if (mb_strlen($username, 'UTF-8') < USERNAME_MIN_LENGTH) {
+        if (mb_strlen($username, DEFAULT_CHARSET) < USERNAME_MIN_LENGTH) {
             return $lang['USERNAME_TOO_SMALL'];
         }
 
@@ -170,10 +170,10 @@ class Validate
         }
 
         // Length
-        if (mb_strlen($password, 'UTF-8') > PASSWORD_MAX_LENGTH) {
+        if (mb_strlen($password, DEFAULT_CHARSET) > PASSWORD_MAX_LENGTH) {
             return sprintf($lang['CHOOSE_PASS_ERR_MAX'], PASSWORD_MAX_LENGTH);
         }
-        if (mb_strlen($password, 'UTF-8') < PASSWORD_MIN_LENGTH) {
+        if (mb_strlen($password, DEFAULT_CHARSET) < PASSWORD_MIN_LENGTH) {
             return sprintf($lang['CHOOSE_PASS_ERR_MIN'], PASSWORD_MIN_LENGTH);
         }
 
diff --git a/styles/templates/admin/index.tpl b/styles/templates/admin/index.tpl
index 0b6155561..fd46b0f1a 100644
--- a/styles/templates/admin/index.tpl
+++ b/styles/templates/admin/index.tpl
@@ -3,8 +3,7 @@
 <!DOCTYPE html>
 <html lang="{$bb_cfg['default_lang']}">
 <head>
-  <meta http-equiv="Content-Type" content="text/html; charset={CONTENT_ENCODING}"/>
-  <meta http-equiv="Content-Style-Type" content="text/css"/>
+  <meta charset="{CONTENT_ENCODING}">
   <link rel="shortcut icon" href="{SITE_URL}favicon.png" type="image/x-icon">
   <title>{L_ADMIN}</title>
 </head>
diff --git a/styles/templates/default/page_header.tpl b/styles/templates/default/page_header.tpl
index 0ec86069b..4fa536406 100644
--- a/styles/templates/default/page_header.tpl
+++ b/styles/templates/default/page_header.tpl
@@ -1,7 +1,7 @@
 <!DOCTYPE html>
 <html lang="{$bb_cfg['default_lang']}">
 <head>
-<meta charset="utf-8">
+<meta charset="{CONTENT_ENCODING}">
 <meta http-equiv="X-UA-Compatible" content="IE=Edge">
 <meta name="viewport" content="initial-scale=1.0">
 <meta name="generator" content="{#APP_NAME#}">