diff --git a/src/milla/dispatch/routing.py b/src/milla/dispatch/routing.py
index c350e49..ff4702f 100644
--- a/src/milla/dispatch/routing.py
+++ b/src/milla/dispatch/routing.py
@@ -205,7 +205,7 @@ class Router(object):
         module ``some.module``.
         '''
 
-        if isinstance(controller, basestring):
+        if not hasattr(controller, '__call__'):
             controller = self._import_controller(controller)
         self.routes.append((self._compile_template(template),
                             controller, vars))