diff --git a/synapse/groups/groups_server.py b/synapse/groups/groups_server.py
index 75634febd0..eac2f41768 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 is_user_in_group or not group.is_public:
+        if not is_user_in_group or not group.is_public:
             raise SynapseError(404, "Unknown group")
 
         if and_is_admin: