diff --git a/sessions/middleware.py b/sessions/middleware.py
index da9b024..4a67bcf 100644
--- a/sessions/middleware.py
+++ b/sessions/middleware.py
@@ -1,24 +1,26 @@
+import datetime
+
+from django.conf import settings
+
 from django.contrib.auth import logout
 from django.contrib import messages
-import datetime
 
-import settings
 
 class SessionIdleTimeout:
-    """Middleware class to timeout a session after a specified time period.
+    """
+    Middleware class to timeout a session after a specified time period.
     """
     def process_request(self, request):
-        # Timeout is done only for authenticated logged in users.
         if request.user.is_authenticated():
-            current_datetime = datetime.datetime.now()
-            
-            # Timeout if idle time period is exceeded.
-            if request.session.has_key('last_activity') and \
-                (current_datetime - request.session['last_activity']).seconds > \
-                settings.SESSION_IDLE_TIMEOUT:
+            now = datetime.datetime.now()
+
+            last_activity = request.session.get('last_activity', now)
+            since = datetime.timedelta.total_seconds(now - last_activity)
+            expired = since > settings.SESSION_IDLE_TIMEOUT
+
+            if expired:
                 logout(request)
-                messages.add_message(request, messages.ERROR, 'Your session has been timed out.')
-            # Set last activity time in current session.
+                messages.error(request, 'Your session has been timed out.')
             else:
-                request.session['last_activity'] = current_datetime
+                request.session['last_activity'] = now
         return None