diff --git a/notebook/notebookapp.py b/notebook/notebookapp.py
index b9d04eefa76..d8668c5a5bc 100755
--- a/notebook/notebookapp.py
+++ b/notebook/notebookapp.py
@@ -265,7 +265,7 @@ def init_settings(self, jupyter_app, kernel_manager, contents_manager,
             # Jupyter stuff
             started=now,
             # place for extensions to register activity
-            activity_sources={},
+            activity_times={},
             jinja_template_vars=jupyter_app.jinja_template_vars,
             nbextensions_path=jupyter_app.nbextensions_path,
             websocket_url=jupyter_app.websocket_url,
@@ -362,7 +362,7 @@ def last_activity(self):
             sources.append(self.settings['terminal_last_activity'])
         except KeyError:
             pass
-        sources.extend(self.settings['activity_sources'].values())
+        sources.extend(self.settings['activity_times'].values())
         return max(sources)
 
 
@@ -1274,7 +1274,7 @@ def init_webapp(self):
             self.session_manager, self.kernel_spec_manager,
             self.config_manager, self.extra_services,
             self.log, self.base_url, self.default_url, self.tornado_settings,
-            self.jinja_environment_options
+            self.jinja_environment_options,
         )
         ssl_options = self.ssl_options
         if self.certfile: