diff --git a/composer.json b/composer.json
index 9ac6ec2e..2f59d0fe 100644
--- a/composer.json
+++ b/composer.json
@@ -16,6 +16,7 @@
         "php": ">=5.2"
     },
     "autoload": {
-        "classmap": ["library/"]
+        "psr-0": { "HTMLPurifier": "library/" },
+        "files": ["library/HTMLPurifier.composer.php"]
     }
 }
diff --git a/library/HTMLPurifier.composer.php b/library/HTMLPurifier.composer.php
new file mode 100644
index 00000000..6706f4e3
--- /dev/null
+++ b/library/HTMLPurifier.composer.php
@@ -0,0 +1,4 @@
+<?php
+if (!defined('HTMLPURIFIER_PREFIX')) {
+    define('HTMLPURIFIER_PREFIX', __DIR__);
+}