diff --git a/admin/environment.xml b/admin/environment.xml
index 55a24fc63d1..6f6fb8141f2 100644
--- a/admin/environment.xml
+++ b/admin/environment.xml
@@ -3008,9 +3008,9 @@
           <ON_ERROR message="iconvrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
-      <PHP_EXTENSION name="mbstring" level="optional">
+      <PHP_EXTENSION name="mbstring" level="required">
         <FEEDBACK>
-          <ON_CHECK message="mbstringrecommended" />
+          <ON_ERROR message="mbstringrequired" />
         </FEEDBACK>
       </PHP_EXTENSION>
       <PHP_EXTENSION name="curl" level="required">
diff --git a/lang/en/admin.php b/lang/en/admin.php
index d60a0844586..8c04357e82b 100644
--- a/lang/en/admin.php
+++ b/lang/en/admin.php
@@ -753,6 +753,7 @@ $string['maxeditingtime'] = 'Maximum time to edit posts';
 $string['maxusersperpage'] = ' Maximum users per page';
 $string['configmaxusersperpage'] = 'Maximum number of users displayed within user selector in course, group, cohort, webservice etc.';
 $string['mbstringrecommended'] = 'Installing the optional MBSTRING library is highly recommended in order to improve site performance, particularly if your site is supporting non-Latin languages.';
+$string['mbstringrequired'] = 'Installing the MBSTRING library is required in order to improve site performance, particularly if your site is supporting non-Latin languages.';
 $string['mediapluginavi'] = 'Enable .avi filter';
 $string['mediapluginflv'] = 'Enable .flv filter';
 $string['mediapluginimg'] = 'Enable auto-embedding of linked images';