diff --git a/warden_server/warden_server.py b/warden_server/warden_server.py
index 51b8cb555c80e216860dce24c6490bddbcb9df99..6e0e5a2c693647825f16920e006a60b910476f48 100755
--- a/warden_server/warden_server.py
+++ b/warden_server/warden_server.py
@@ -1637,6 +1637,7 @@ class WardenHandler(ObjectBase):
         clients_dict = [c._asdict() for c in clients]
         for c in clients_dict:
             del c['secret']
+            c['registered'] = c['registered'].isoformat() + 'Z'
         return {"clients": clients_dict}
 
     @expose(read=True)