diff --git a/lib/tiles/offlineTilesEnabler.js b/lib/tiles/offlineTilesEnabler.js
index e248bd8..1635ac3 100644
--- a/lib/tiles/offlineTilesEnabler.js
+++ b/lib/tiles/offlineTilesEnabler.js
@@ -32,7 +32,8 @@ define([
             {
                 console.log("extending layer", layer.url);
 
-                layer._lastTileUrl = "";                
+                layer._lastTileUrl = "";
+                layer._imageType = "";
 
                 /* we add some methods to the layer object */
                 /* we don't want to extend the tiled layer class, as it is a capability that we want to add only to one instance */
@@ -76,6 +77,7 @@ define([
 console.log("LIBRARY ONLINE " + this.offline.online)
                     if( this.offline.online )
                     {
+                        if(layer._imageType == "")layer._imageType = this.tileInfo.format.toLowerCase();
                         console.log("fetching url online: ", url);
                         layer._lastTileUrl = url;
                         return url;
@@ -99,7 +101,7 @@ console.log("LIBRARY ONLINE " + this.offline.online)
                         {
                             img.style.borderColor = "blue";
                             console.log("found tile offline", url);
-                            imgURL = "data:image;base64," + offlineTile.img;
+                            imgURL = "data:image/" + layer._imageType +";base64," + offlineTile.img;
                         }
                         else
                         {