diff --git a/lib/marked.js b/lib/marked.js
index 1859d268b6..69a30dcc90 100644
--- a/lib/marked.js
+++ b/lib/marked.js
@@ -5,6 +5,7 @@
  */
 
 ;(function() {
+'use strict';
 
 /**
  * Block-Level Grammar
@@ -1144,8 +1145,8 @@ function resolveUrl(base, href) {
     return base + href;
   }
 }
-baseUrls = {};
-originIndependentUrl = /^$|^[a-z][a-z0-9+.-]*:|^[?#]/i;
+var baseUrls = {};
+var originIndependentUrl = /^$|^[a-z][a-z0-9+.-]*:|^[?#]/i;
 
 function noop() {}
 noop.exec = noop;