diff --git a/ckanext/privatedatasets/plugin.py b/ckanext/privatedatasets/plugin.py
index 71c18d4..714a2dc 100644
--- a/ckanext/privatedatasets/plugin.py
+++ b/ckanext/privatedatasets/plugin.py
@@ -199,7 +199,7 @@ class PrivateDatasets(p.SingletonPlugin, tk.DefaultDatasetForm):
                      'use_cache': False},
                     {'id': package_id})
                 # Prevent acquired datasets jumping to the first position
-                new_pkg_dict['metadata_modified'] = new_pkg_dict['revision_timestamp']
+                new_pkg_dict['metadata_modified'] = new_pkg_dict.get('revision_timestamp', '')
                 self.indexer.update_dict(new_pkg_dict)
 
         return pkg_dict
diff --git a/ckanext/privatedatasets/tests/test_plugin.py b/ckanext/privatedatasets/tests/test_plugin.py
index ff7fd68..b32f696 100644
--- a/ckanext/privatedatasets/tests/test_plugin.py
+++ b/ckanext/privatedatasets/tests/test_plugin.py
@@ -282,8 +282,10 @@ class PluginTest(unittest.TestCase):
         package_id = 'package_id'
 
         # Configure mocks
-        default_dict = {'a': '0', 'b': 1, 'm': True}
-        package_show = MagicMock(return_value=default_dict)
+        default_dict = {'a': '0', 'b': 1, 'm': True, 'revision_timestamp': '2000'}
+        expected_dict = default_dict.copy()
+        expected_dict['metadata_modified'] = default_dict['revision_timestamp']
+        package_show = MagicMock(return_value=default_dict.copy())
         plugin.tk.get_action = MagicMock(return_value=package_show)
 
         # Each time 'AllowedUser' is called, we must get a new instance
@@ -336,7 +338,7 @@ class PluginTest(unittest.TestCase):
             self.assertEquals(0, self.privateDatasets.indexer.update_dict.call_count)
         else:
             # Check that the cache has been updated
-            self.privateDatasets.indexer.update_dict.assert_called_once_with(default_dict)
+            self.privateDatasets.indexer.update_dict.assert_called_once_with(expected_dict)
 
     @parameterized.expand([
         # One element