diff --git a/lib/types.js b/lib/types.js
index 2af4fd7..54811c7 100644
--- a/lib/types.js
+++ b/lib/types.js
@@ -52,7 +52,7 @@ var _types = {
     'CAL-ADDRESS': {
         format: function(value) {
             var v = value.toString();
-            if(v.lastIndexOf("mailto:") != 0)
+            if(v.indexOf("mailto:") === -1)
                 v = "mailto:"+v;
             return v;
         }