diff --git a/composer.json b/composer.json
index b6b836a..cd1eefe 100644
--- a/composer.json
+++ b/composer.json
@@ -20,7 +20,7 @@
     ],
     "require": {
         "php": ">=5.3.2",
-        "ext-mbstring": "*"
+        "symfony/polyfill-mbstring": "^1.0"
     },
     "require-dev": {
         "phpunit/phpunit": "3.7.*",