diff --git a/lib/html-min.cls.php b/lib/html-min.cls.php
index e8fd4d781..1e11b78bb 100644
--- a/lib/html-min.cls.php
+++ b/lib/html-min.cls.php
@@ -17,6 +17,11 @@
 
 class HTML_MIN
 {
+	/**
+	 * @var string
+	 */
+	protected $_html = '';
+
 	/**
 	 * @var boolean
 	 */