diff --git a/phpBB/composer.json b/phpBB/composer.json
index 31ad38a6b4..d5acd3112c 100644
--- a/phpBB/composer.json
+++ b/phpBB/composer.json
@@ -27,6 +27,7 @@
 	"require": {
 		"php": "^7.1.3",
 		"ext-json": "*",
+		"ext-mbstring": "*",
 		"bantu/ini-get-wrapper": "~1.0",
 		"google/recaptcha": "~1.1",
 		"guzzlehttp/guzzle": "~6.3",
diff --git a/phpBB/language/en/install.php b/phpBB/language/en/install.php
index 530c003026..bb8e28e83a 100644
--- a/phpBB/language/en/install.php
+++ b/phpBB/language/en/install.php
@@ -112,6 +112,8 @@ $lang = array_merge($lang, array(
 	'PCRE_UTF_SUPPORT_EXPLAIN'			=> 'phpBB will not run if your PHP installation is not compiled with UTF-8 support in the PCRE extension.',
 	'PHP_JSON_SUPPORT'					=> 'PHP JSON support',
 	'PHP_JSON_SUPPORT_EXPLAIN'			=> 'In order for phpBB to function correctly, the PHP JSON extension needs to be available.',
+	'PHP_MBSTRING_SUPPORT'				=> 'PHP mbstring support',
+	'PHP_MBSTRING_SUPPORT_EXPLAIN'		=> 'In order for phpBB to function correctly, the PHP mbstring extension needs to be available.',
 	'PHP_XML_SUPPORT'					=> 'PHP XML/DOM support',
 	'PHP_XML_SUPPORT_EXPLAIN'			=> 'In order for phpBB to function correctly, the PHP XML/DOM extension needs to be available.',
 	'PHP_SUPPORTED_DB'					=> 'Supported databases',
diff --git a/phpBB/phpbb/install/module/requirements/task/check_server_environment.php b/phpBB/phpbb/install/module/requirements/task/check_server_environment.php
index 41aa82623b..8f8b0e1934 100644
--- a/phpBB/phpbb/install/module/requirements/task/check_server_environment.php
+++ b/phpBB/phpbb/install/module/requirements/task/check_server_environment.php
@@ -14,7 +14,7 @@
 namespace phpbb\install\module\requirements\task;
 
 /**
- * Installer task that checks if the server meats phpBB requirements
+ * Installer task that checks if the server meets phpBB requirements
  */
 class check_server_environment extends \phpbb\install\task_base
 {
@@ -71,6 +71,9 @@ class check_server_environment extends \phpbb\install\task_base
 		// Check for JSON support
 		$this->check_json();
 
+		// Check for mbstring support
+		$this->check_mbstring();
+
 		// XML extension support check
 		$this->check_xml();
 
@@ -155,6 +158,22 @@ class check_server_environment extends \phpbb\install\task_base
 		$this->set_test_passed(false);
 	}
 
+	/**
+	 * Checks whether PHP's mbstring extension is available or not
+	 */
+	protected function check_mbstring()
+	{
+		if (@extension_loaded('mbstring'))
+		{
+			$this->set_test_passed(true);
+			return;
+		}
+
+		$this->response_helper->add_error_message('PHP_MBSTRING_SUPPORT', 'PHP_MBSTRING_SUPPORT_EXPLAIN');
+
+		$this->set_test_passed(false);
+	}
+
 	/**
 	 * Checks whether or not the XML PHP extension is available (Required by the text formatter)
 	 */