diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 042c8f2..bd7417d 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -185,6 +185,7 @@ function system_requirements($phase) {
     'gd',
     'hash',
     'json',
+    'mbstring',
     'pcre',
     'pdo',
     'session',