diff --git a/composer.json b/composer.json
index 547e0b89a..f6745474d 100644
--- a/composer.json
+++ b/composer.json
@@ -1,5 +1,6 @@
 {
     "require": {
+        "ext-mbstring": "*",
         "ircmaxell/password-compat": "1.0.3",
         "fguillot/simple-validator": "dev-master",
         "swiftmailer/swiftmailer": "@stable",