diff --git a/phpBB/assets/javascript/installer.js b/phpBB/assets/javascript/installer.js
index a11b76b863..cfe685f88b 100644
--- a/phpBB/assets/javascript/installer.js
+++ b/phpBB/assets/javascript/installer.js
@@ -605,6 +605,8 @@
 	function interceptFormSubmit($form) {
 		if (!$form.length) {
 			return;
+		} else if ($form.find('input[name="admin_name"]').length > 0) {
+			setAdminTimezone($form);
 		}
 
 		$form.find(':submit').bind('click', function (event) {
@@ -612,4 +614,20 @@
 			submitForm($form, $(this));
 		});
 	}
+
+	/**
+	 * Set admin timezone in form
+	 *
+	 * @param $form
+	 */
+	function setAdminTimezone($form) {
+		// Set admin timezone if it does not exist yet
+		if ($form.find('input[name="admin_timezone"]').length === 0) {
+			const timeZone = Intl.DateTimeFormat().resolvedOptions().timeZone;
+
+			// Add timezone as form entry
+			const timezoneEntry = $('<input type="hidden" name="admin_timezone" value="' + timeZone + '">');
+			$form.append(timezoneEntry);
+		}
+	}
 })(jQuery); // Avoid conflicts with other libraries
diff --git a/phpBB/phpbb/install/module/install_database/task/add_config_settings.php b/phpBB/phpbb/install/module/install_database/task/add_config_settings.php
index bd3f0852e6..5b9a9da536 100644
--- a/phpBB/phpbb/install/module/install_database/task/add_config_settings.php
+++ b/phpBB/phpbb/install/module/install_database/task/add_config_settings.php
@@ -132,6 +132,7 @@ class add_config_settings extends database_task
 
 		$updates = [
 			'board_startdate' => (string) $current_time,
+			'board_timezone' => $this->install_config->get('admin_timezone'),
 			'default_lang' => $this->install_config->get('default_lang'),
 
 			'server_name' => $this->install_config->get('server_name'),
diff --git a/phpBB/phpbb/install/module/install_database/task/update_user_and_post_data.php b/phpBB/phpbb/install/module/install_database/task/update_user_and_post_data.php
index ba178135b9..7cc5fd4f49 100644
--- a/phpBB/phpbb/install/module/install_database/task/update_user_and_post_data.php
+++ b/phpBB/phpbb/install/module/install_database/task/update_user_and_post_data.php
@@ -114,7 +114,8 @@ class update_user_and_post_data extends database_task
 			. '		user_lang = :lang,'
 			. '		user_email = :email,'
 			. '		user_dateformat = :dateformat,'
-			. '		username_clean = :clean_username'
+			. '		username_clean = :clean_username,'
+			. '		user_timezone = :timezone'
 			. ' WHERE username = \'Admin\'';
 
 		$this->create_and_execute_prepared_stmt($sql, [
@@ -125,6 +126,7 @@ class update_user_and_post_data extends database_task
 			'email'				=> $this->install_config->get('board_email'),
 			'dateformat'		=> $this->language->lang('default_dateformat'),
 			'clean_username'	=> utf8_clean_string($this->install_config->get('admin_name')),
+			'timezone'			=> $this->install_config->get('admin_timezone'),
 		]);
 		$this->exec_sql('UPDATE ' . $this->user_table . ' SET user_regdate = ' . $current_time);
 
diff --git a/phpBB/phpbb/install/module/obtain_data/task/obtain_admin_data.php b/phpBB/phpbb/install/module/obtain_data/task/obtain_admin_data.php
index 0560f2d46d..1175ab8626 100644
--- a/phpBB/phpbb/install/module/obtain_data/task/obtain_admin_data.php
+++ b/phpBB/phpbb/install/module/obtain_data/task/obtain_admin_data.php
@@ -71,6 +71,7 @@ class obtain_admin_data extends \phpbb\install\task_base implements \phpbb\insta
 		$admin_pass1	= $this->io_handler->get_input('admin_pass1', '', true);
 		$admin_pass2	= $this->io_handler->get_input('admin_pass2', '', true);
 		$board_email	= $this->io_handler->get_input('board_email', '', true);
+		$admin_timezone	= $this->io_handler->get_input('admin_timezone', 'UTC', true);
 
 		$admin_data_valid = $this->check_admin_data($admin_name, $admin_pass1, $admin_pass2, $board_email);
 
@@ -79,6 +80,7 @@ class obtain_admin_data extends \phpbb\install\task_base implements \phpbb\insta
 			$this->install_config->set('admin_name', $admin_name);
 			$this->install_config->set('admin_passwd', $admin_pass1);
 			$this->install_config->set('board_email', $board_email);
+			$this->install_config->set('admin_timezone', $admin_timezone);
 		}
 		else
 		{