diff --git a/README.md b/README.md
index 5d3d1ad..ee4b101 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 ![Website screenshot](http://i.imgur.com/gKZezVc.png)
 
-**ts-website - free website for your TeamSpeak 3  server**<br>
+**ts-website - free website for your TeamSpeak 3 server**<br>
 
 #### Useful links
 - [Demo](https://ts.wruczek.top/)
@@ -19,7 +19,8 @@
 
 ### Requirements
 - Minimum
- - PHP 5.3.0 or newer
+ - PHP 5.4 or newer
+ - Installed and enabled ``mbstring`` extension
 - Recommended
  - Newest stable PHP version
  - Up-to-date Apache server
diff --git a/include/modulecheck.php b/include/modulecheck.php
index 679cfe6..0a8a1ee 100644
--- a/include/modulecheck.php
+++ b/include/modulecheck.php
@@ -36,13 +36,24 @@ function isPHPVersionSupported() {
         define('PHP_VERSION_ID', ($version[0] * 10000 + $version[1] * 100 + $version[2]));
     }
 
-    return PHP_VERSION_ID >= 50300;
+    return PHP_VERSION_ID >= 50400;
 }
 
 if (!isPHPVersionSupported()) {
     $title = 'Unsupported PHP version';
 
-    $text = '<p>You are using old, unsupported PHP version.</p><p>Your PHP version: <b>' . phpversion() . '</b>, required PHP version: <b>5.3.0</b>.</p><p>Please update your PHP installation and try again.</p>';
+    $text = '<p>You are using old, unsupported PHP version.</p><p>Your PHP version: <b>' . phpversion() . '</b>, required PHP version: <b>5.4.0</b>.</p><p>Please update your PHP installation and try again.</p>';
+
+    die(showError($title, $text));
+}
+
+if (!extension_loaded("mbstring")) {
+
+    $title = 'MBString extension is missing';
+
+    $text = '<p>Required PHP extension: <code>mbstring</code> has not been found on the server.</p>
+            <p>Follow <a href="http://askubuntu.com/a/772505">this instructions</a> if you are using Ubuntu 16.04 with PHP 7.0 (recommended). Otherwise, installation instructions can be found <a href="https://www.google.pl/?q=install+mbstring+(your+operating+system)">on Google</a> ;)</p>
+            <p>If you are using Web Hosting service, please contact the Hosting support for instruction on enabling mbstring.</p>';
 
     die(showError($title, $text));
 }