diff --git a/lib/tiles/offlineEnabler.js b/lib/tiles/offlineEnabler.js
index 26136bd..afd1aca 100644
--- a/lib/tiles/offlineEnabler.js
+++ b/lib/tiles/offlineEnabler.js
@@ -287,19 +287,31 @@ define([
 
 				/* internal methods */
 
+                /**
+                 * Makes a request to a tile url and uses that as a basis for the
+                 * the average tile size.
+                 * Future Iterations could call multiple tiles and do an actual average.
+                 * @param callback
+                 * @returns {Number} Returns NaN if there was a problem retrieving the tile
+                 */
 				layer.estimateTileSize = function(callback)
 				{
-                    var url = this.offline.proxyPath + "?" +  layer._tileUrlArr[0];
-                    var size = 0;
-                    request.get(url,{
-                        handleAs: "text/plain; charset=x-user-defined",
-                        headers: {                     // This is required to stop the
-                            "X-Requested-With": "" // server from rejecting the
-                        }
-                    }).then(function(response){
-                            var img = Base64Utils.wordToBase64(Base64Utils.stringToWord(response));
-                            callback(img.length + url.length);
-                    });
+                    if(layer._tileUrlArr.length > 0){
+                        var url = this.offline.proxyPath + "?" +  layer._tileUrlArr[0];
+                        request.get(url,{
+                            handleAs: "text/plain; charset=x-user-defined",
+                            headers: {
+                                "X-Requested-With": "" //bypasses a dojo xhr bug
+                            }
+                        }).then(function(response){
+                                var img = Base64Utils.wordToBase64(Base64Utils.stringToWord(response));
+                                callback(img.length + url.length);
+                            });
+                    }
+                    else{
+                        return NaN;
+                    }
+
 				};
 
 				layer.doNextTile = function(i, cells, reportProgress)