diff --git a/docs/timeline.html b/docs/timeline.html
index 544aa463..613ae09f 100644
--- a/docs/timeline.html
+++ b/docs/timeline.html
@@ -915,7 +915,7 @@ var options = {
 </p>
 <ul>
   <li><code>item</code>: the item being manipulated</li>
-  <li><code>callback</code>: a callback function which must be invoked to report back. The callback must be invoked as <code>callback(item | null)</code>. Here, <code>item</code> can contain changes to the passed item. When invoked as <code>callback(null)</code>, the action will be cancelled.</li>
+  <li><code>callback</code>: a callback function which must be invoked to report back. The callback must be invoked as <code>callback(item | null)</code>. Here, <code>item</code> can contain changes to the passed item. Parameter `item` typically contains fields `content`, `start`, and optionally `end`. The type of `start` and `end` is determined by the DataSet type configuration and is `Date` by default.  When invoked as <code>callback(null)</code>, the action will be cancelled.</li>
 </ul>
 
 <p>
diff --git a/examples/timeline/02_interactive.html b/examples/timeline/02_interactive.html
index 32d8f97d..0c4f6d36 100644
--- a/examples/timeline/02_interactive.html
+++ b/examples/timeline/02_interactive.html
@@ -22,10 +22,7 @@
 <script>
   // create a dataset with items
   var items = new vis.DataSet({
-    type: {
-      start: 'Date',
-      end: 'Date'
-    }
+    type: { start: 'ISODate', end: 'ISODate' }
   });
   items.add([
     {id: 1, content: 'item 1<br>start', start: '2014-01-23'},
diff --git a/examples/timeline/03_a_lot_of_data.html b/examples/timeline/03_a_lot_of_data.html
index 287136a9..93cb7957 100644
--- a/examples/timeline/03_a_lot_of_data.html
+++ b/examples/timeline/03_a_lot_of_data.html
@@ -31,10 +31,7 @@
   // create a dataset with items
   var now = moment().minutes(0).seconds(0).milliseconds(0);
   var items = new vis.DataSet({
-    type: {
-      start: 'Date',
-      end: 'Date'
-    }
+    type: {start: 'ISODate', end: 'ISODate' }
   });
 
   // create data
diff --git a/examples/timeline/06_event_listeners.html b/examples/timeline/06_event_listeners.html
index f64b575a..df240ce4 100644
--- a/examples/timeline/06_event_listeners.html
+++ b/examples/timeline/06_event_listeners.html
@@ -18,10 +18,7 @@
   <div id="log"></div>
 
   <script type="text/javascript">
-    var items = new vis.DataSet({
-      type: { start: 'Date', end: 'Date' }
-    });
-    items.add([
+    var items = new vis.DataSet([
       {id: 1, content: 'item 1', start: '2013-04-20'},
       {id: 2, content: 'item 2', start: '2013-04-14'},
       {id: 3, content: 'item 3', start: '2013-04-18'},
diff --git a/src/DataSet.js b/src/DataSet.js
index d1ee3d2b..41dcafd1 100644
--- a/src/DataSet.js
+++ b/src/DataSet.js
@@ -48,9 +48,11 @@ function DataSet (data, options) {
   this.options = options || {};
   this.data = {};                                 // map with data indexed by id
   this.fieldId = this.options.fieldId || 'id';    // name of the field containing id
-  this.type = {};                                 // field types by field name
+  this.type = {};                                 // internal field types (NOTE: this can differ from this.options.type)
   this.showInternalIds = this.options.showInternalIds || false; // show internal ids with the get function
 
+  // all variants of a Date are internally stored as Date, so we can convert
+  // from everything to everything (also from ISODate to Number for example)
   if (this.options.type) {
     for (var field in this.options.type) {
       if (this.options.type.hasOwnProperty(field)) {
diff --git a/src/timeline/Timeline.js b/src/timeline/Timeline.js
index 780ccf38..1b7d4540 100644
--- a/src/timeline/Timeline.js
+++ b/src/timeline/Timeline.js
@@ -413,20 +413,22 @@ Timeline.prototype.getItemRange = function() {
   if (itemsData) {
     // calculate the minimum value of the field 'start'
     var minItem = itemsData.min('start');
-    min = minItem ? minItem.start.valueOf() : null;
+    min = minItem ? util.convert(minItem.start, 'Date').valueOf() : null;
+    // Note: we convert first to Date and then to number because else
+    // a conversion from ISODate to Number will fail
 
     // calculate maximum value of fields 'start' and 'end'
     var maxStartItem = itemsData.max('start');
     if (maxStartItem) {
-      max = maxStartItem.start.valueOf();
+      max = util.convert(maxStartItem.start, 'Date').valueOf();
     }
     var maxEndItem = itemsData.max('end');
     if (maxEndItem) {
       if (max == null) {
-        max = maxEndItem.end.valueOf();
+        max = util.convert(maxEndItem.end, 'Date').valueOf();
       }
       else {
-        max = Math.max(max, maxEndItem.end.valueOf());
+        max = Math.max(max, util.convert(maxEndItem.end, 'Date').valueOf());
       }
     }
   }
diff --git a/src/timeline/component/ItemSet.js b/src/timeline/component/ItemSet.js
index 95c5ed86..2f908afd 100644
--- a/src/timeline/component/ItemSet.js
+++ b/src/timeline/component/ItemSet.js
@@ -50,6 +50,11 @@ function ItemSet(body, options) {
   // options is shared by this ItemSet and all its items
   this.options = util.extend({}, this.defaultOptions);
 
+  // options for getting items from the DataSet with the correct type
+  this.itemOptions = {
+    type: {start: 'Date', end: 'Date'}
+  };
+
   this.conversion = {
     toScreen: body.util.toScreen,
     toTime: body.util.toTime
@@ -650,7 +655,7 @@ ItemSet.prototype._onUpdate = function(ids) {
   var me = this;
 
   ids.forEach(function (id) {
-    var itemData = me.itemsData.get(id),
+    var itemData = me.itemsData.get(id, me.itemOptions),
         item = me.items[id],
         type = itemData.type ||
             (itemData.start && itemData.end && 'range') ||
@@ -1070,16 +1075,18 @@ ItemSet.prototype._onDragEnd = function (event) {
 
     this.touchParams.itemProps.forEach(function (props) {
       var id = props.item.id,
-          itemData = me.itemsData.get(id);
+          itemData = me.itemsData.get(id, me.itemOptions);
 
       var changed = false;
       if ('start' in props.item.data) {
         changed = (props.start != props.item.data.start.valueOf());
-        itemData.start = util.convert(props.item.data.start, dataset.convert['start']);
+        itemData.start = util.convert(props.item.data.start,
+                dataset.options.type && dataset.options.type.start || 'Date');
       }
       if ('end' in props.item.data) {
         changed = changed  || (props.end != props.item.data.end.valueOf());
-        itemData.end = util.convert(props.item.data.end, dataset.convert['end']);
+        itemData.end = util.convert(props.item.data.end,
+                dataset.options.type && dataset.options.type.end || 'Date');
       }
       if ('group' in props.item.data) {
         changed = changed  || (props.group != props.item.data.group);
diff --git a/src/util.js b/src/util.js
index a68c3455..522b5241 100644
--- a/src/util.js
+++ b/src/util.js
@@ -319,8 +319,7 @@ util.convert = function(object, type) {
       }
 
     default:
-      throw new Error('Cannot convert object of type ' + util.getType(object) +
-          ' to type "' + type + '"');
+      throw new Error('Unknown type "' + type + '"');
   }
 };
 
diff --git a/test/timeline.html b/test/timeline.html
index f28dcfa7..14ce8d91 100644
--- a/test/timeline.html
+++ b/test/timeline.html
@@ -58,9 +58,9 @@
   // create a dataset with items
   var now = moment().minutes(0).seconds(0).milliseconds(0);
   var items = new vis.DataSet({
-    convert: {
-      start: 'Date',
-      end: 'Date'
+    type: {
+      start: 'ISODate',
+      end: 'ISODate'
     },
     fieldId: '_id'
   });