diff --git a/composer.json b/composer.json
index 1439b82..167ed6f 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,11 @@
             "homepage": "http://erusev.com"
         }
     ],
+    "require": {
+        "php": ">=5.3.3",
+        "ext-mbstring": "*"
+    },
     "autoload": {
         "psr-0": {"Parsedown": ""}
     }
-}
\ No newline at end of file
+}