diff --git a/app/routes/admin.py b/app/routes/admin.py
index c76a3dd..0901a55 100644
--- a/app/routes/admin.py
+++ b/app/routes/admin.py
@@ -95,8 +95,10 @@ async def get_stats(admin_user: User = Depends(get_admin_user)):
     top_users = list(users_collection.aggregate([
         {"$lookup": {
             "from": "pins",
-            "localField": "_id",
-            "foreignField": "user_id",
+            "let": { "user_id": { "$toString": "$_id" } },
+            "pipeline": [
+                { "$match": { "$expr": { "$eq": ["$user_id", "$$user_id"] } } }
+            ],
             "as": "pins"
         }},
         {"$project": {