diff --git a/composer.json b/composer.json
index a280b88..c95c133 100644
--- a/composer.json
+++ b/composer.json
@@ -23,6 +23,7 @@
     ],
     "require": {
         "php": ">=5.2.0",
+        "ext-mbstring": "*",
         "ext-xml": "*",
         "ext-xmlwriter": "*"
     },