diff --git a/bin/core/src/api/write/user_group.rs b/bin/core/src/api/write/user_group.rs
index 20107c460..49b735f4e 100644
--- a/bin/core/src/api/write/user_group.rs
+++ b/bin/core/src/api/write/user_group.rs
@@ -141,7 +141,7 @@ impl Resolve<AddUserToUserGroup, User> for State {
     db.user_groups
       .update_one(
         filter.clone(),
-        doc! { "$push": { "users": &user.id } },
+        doc! { "$addToSet": { "users": &user.id } },
         None,
       )
       .await