diff --git a/composer.json b/composer.json
index a74b573..e490c61 100644
--- a/composer.json
+++ b/composer.json
@@ -25,6 +25,7 @@
     }],
     "require": {
         "php": ">=5.3.3",
+        "ext-mbstring": "*",
         "psr/log": "^1.0"
     },
     "require-dev": {