diff --git a/phpBB/includes/acp/acp_board.php b/phpBB/includes/acp/acp_board.php
index 70d0c8cf58..8e571de379 100644
--- a/phpBB/includes/acp/acp_board.php
+++ b/phpBB/includes/acp/acp_board.php
@@ -193,7 +193,7 @@ class acp_board
 						'allow_post_flash'		=> array('lang' => 'ALLOW_POST_FLASH',		'validate' => 'bool',	'type' => 'radio:yes_no', 'explain' => true),
 						'allow_smilies'			=> array('lang' => 'ALLOW_SMILIES',			'validate' => 'bool',	'type' => 'radio:yes_no', 'explain' => false),
 						'allow_post_links'		=> array('lang' => 'ALLOW_POST_LINKS',		'validate' => 'bool',	'type' => 'radio:yes_no', 'explain' => true),
-						'allowed_schemes_links'	=> array('lang' => 'ALLOWED_SCHEMES_LINKS',	'validate' => 'string',	'type' => 'text:0:255', 'explain' => true),
+						'allowed_schemes_links'	=> array('lang' => 'ALLOWED_SCHEMES_LINKS',	'validate' => 'csv',	'type' => 'text:0:255', 'explain' => true),
 						'allow_nocensors'		=> array('lang' => 'ALLOW_NO_CENSORS',		'validate' => 'bool',	'type' => 'radio:yes_no', 'explain' => true),
 						'allow_bookmarks'		=> array('lang' => 'ALLOW_BOOKMARKS',		'validate' => 'bool',	'type' => 'radio:yes_no', 'explain' => true),
 						'enable_post_confirm'	=> array('lang' => 'VISUAL_CONFIRM_POST',	'validate' => 'bool',	'type' => 'radio:yes_no', 'explain' => true),
@@ -497,6 +497,19 @@ class acp_board
 		$cfg_array = (isset($_REQUEST['config'])) ? $request->variable('config', array('' => ''), true) : $this->new_config;
 		$error = array();
 
+		// Prevalidate allowed URL schemes
+		if ($mode == 'post')
+		{
+			$schemes = array_filter(explode(',', $cfg_array['allowed_schemes_links']));
+			foreach ($schemes as $scheme)
+			{
+				if (!preg_match('#^[a-z][a-z0-9+\\-.]*$#Di', $scheme))
+				{
+					$error[] = $language->lang('URL_SCHEME_INVALID', $language->lang('ALLOWED_SCHEMES_LINKS'), $scheme);
+				}
+			}
+		}
+
 		// We validate the complete config if wished
 		validate_config_vars($display_vars['vars'], $cfg_array, $error);
 
diff --git a/phpBB/includes/functions_acp.php b/phpBB/includes/functions_acp.php
index a013af2c89..7c6eebb5a8 100644
--- a/phpBB/includes/functions_acp.php
+++ b/phpBB/includes/functions_acp.php
@@ -453,8 +453,20 @@ function validate_config_vars($config_vars, &$cfg_array, &$error)
 					$error[] = $language->lang('URL_INVALID', $language->lang($config_definition['lang']));
 				}
 
+				goto validate_string;
+
+			case 'csv':
+				// Validate comma separated values
+				$unfiltered_array = explode(',', $cfg_array[$config_name]);
+				$filtered_array = array_filter($unfiltered_array);
+				if (!empty($filtered_array) && count($unfiltered_array) !== count($filtered_array))
+				{
+					$error[] = $language->lang('CSV_INVALID', $language->lang($config_definition['lang']));
+				}
+
 			// no break here
 
+			validate_string:
 			case 'string':
 				$length = utf8_strlen($cfg_array[$config_name]);
 
diff --git a/phpBB/language/en/acp/common.php b/phpBB/language/en/acp/common.php
index 3705678112..29d0ec5947 100644
--- a/phpBB/language/en/acp/common.php
+++ b/phpBB/language/en/acp/common.php
@@ -235,6 +235,7 @@ $lang = array_merge($lang, array(
 	'CRON_NO_SUCH_TASK'		=> 'Could not find cron task “%s”.',
 	'CRON_NO_TASK'			=> 'No cron tasks need to be run right now.',
 	'CRON_NO_TASKS'			=> 'No cron tasks could be found.',
+	'CSV_INVALID'			=> 'The provided comma-separated setting “%1$s” is invalid. The values should be delimited by comma only, it should not contain any leading or trailing delimiters.',
 	'CURRENT_VERSION'		=> 'Current version',
 
 	'DEACTIVATE'				=> 'Deactivate',
@@ -316,6 +317,7 @@ $lang = array_merge($lang, array(
 
 	'UCP'					=> 'User Control Panel',
 	'URL_INVALID'			=> 'The provided URL for the setting “%1$s” is invalid.',
+	'URL_SCHEME_INVALID'	=> 'The provided scheme “%2$s” in comma-separated setting “%1$s” is invalid. Scheme should start with a latin character followed by alphanumeric characters, hyphens or dots.',
 	'USERNAMES_EXPLAIN'		=> 'Place each username on a separate line.',
 	'USER_CONTROL_PANEL'	=> 'User Control Panel',
 
diff --git a/phpBB/phpbb/textformatter/s9e/factory.php b/phpBB/phpbb/textformatter/s9e/factory.php
index 7d12abad90..eadd1ba2de 100644
--- a/phpBB/phpbb/textformatter/s9e/factory.php
+++ b/phpBB/phpbb/textformatter/s9e/factory.php
@@ -218,7 +218,9 @@ class factory implements \phpbb\textformatter\cache_interface
 		{
 			$configurator->urlConfig->disallowScheme($scheme);
 		}
-		foreach (array_filter(explode(',', $this->config['allowed_schemes_links'])) as $scheme)
+
+		$schemes = array_filter(explode(',', $this->config['allowed_schemes_links']));
+		foreach ($schemes as $scheme)
 		{
 			$configurator->urlConfig->allowScheme(trim($scheme));
 		}