diff --git a/zimsoap/client.py b/zimsoap/client.py
index 9997ab5..850da62 100644
--- a/zimsoap/client.py
+++ b/zimsoap/client.py
@@ -296,7 +296,7 @@ def delegated_login(self, login, admin_zc, duration=0):
         selector = zobjects.Account(name=login).to_selector()
         delegate_args = {'account': selector}
         if duration:
-            delegate_args['duration': duration]
+            delegate_args['duration'] = duration
         resp = admin_zc.request('DelegateAuth', delegate_args)
 
         lifetime = resp['lifetime']