diff --git a/lib/cartodb/server_options.js b/lib/cartodb/server_options.js
index 86c607f3..fb7b8422 100644
--- a/lib/cartodb/server_options.js
+++ b/lib/cartodb/server_options.js
@@ -159,13 +159,10 @@ module.exports = function(){
         callback(null, me.channelCache[cacheKey]);
         return;
       } 
-
-      if ( req.params.token ) {
-        if ( ! me.channelCache.hasOwnProperty(cacheKey) ) {
-          callback(new Error('missing channel cache for token ' + req.params.token));
-        } else {
-          callback(null, me.channelCache[cacheKey]);
-        }
+      else if ( req.params.token ) {
+        // cached cache channel for token-based access should be constructed
+        // at cache creation time
+        callback(new Error('missing channel cache for token ' + req.params.token));
         return;
       }
 
@@ -219,12 +216,15 @@ module.exports = function(){
         }
 
         // Set Last-Modified header
-        //
-        // Currently sets it to NOW
-        //
-        // TODO: find out a real value, querying for most recent change in
-        //       any of the source tables
-        res.header('Last-Modified', new Date().toUTCString());
+        var lastUpdated;
+        if ( req.params.cache_buster ) {
+          // Assuming cache_buster is a timestamp
+          // FIXME: store lastModified in the cache channel instead
+          lastUpdated = new Date(parseInt(req.params.cache_buster));
+        } else {
+          lastUpdated = new Date();
+        }
+        res.header('Last-Modified', lastUpdated.toUTCString());
 
         me.generateCacheChannel(req, function(err, channel){
             if ( ! err ) {