diff --git a/lib/runkeeper.js b/lib/runkeeper.js
index 2ceda91..b56dbd6 100644
--- a/lib/runkeeper.js
+++ b/lib/runkeeper.js
@@ -139,6 +139,8 @@ HealthGraph.prototype.apiCall = function(opts, callback) {
  * If passed opts.get_next it will get all items of the activity feed until there is no more
  * `data.next`.
  *
+ * If passed opts.modified_since you might get an empty response (304 Not Modified). In those cases callback(null, []) will be called
+ *
  * @param {Object}   opts     (Optional) Gets extended by `resources.fitnessActivityFeed`.
  * @param {Function} callback Given err and data.
  */
@@ -157,6 +159,7 @@ HealthGraph.prototype.activityFeed = function(opts, callback) {
 
     this.apiCall(opts, function(err, data) {
       if (err) return callback(err, null);
+      if (!data.items) return callback(null, []);
 
       if (data.next) {
         opts.items = data.items.concat(opts.items);