diff --git a/synapse/groups/groups_server.py b/synapse/groups/groups_server.py
index 175ff433a..4f9e45913 100644
--- a/synapse/groups/groups_server.py
+++ b/synapse/groups/groups_server.py
@@ -69,7 +69,7 @@ class GroupsServerHandler(object):
             raise SynapseError(404, "Unknown group")
 
         is_user_in_group = yield self.store.is_user_in_group(requester_user_id, group_id)
-        if group and not is_user_in_group and not group.is_public:
+        if group and not is_user_in_group and not group["is_public"]:
             raise SynapseError(404, "Unknown group")
 
         if and_is_admin: