diff --git a/website/common/script/ops/buy/purchase.js b/website/common/script/ops/buy/purchase.js
index 67b65224eb..02c00dec26 100644
--- a/website/common/script/ops/buy/purchase.js
+++ b/website/common/script/ops/buy/purchase.js
@@ -64,7 +64,10 @@ function purchaseItem (user, item, price, type, key) {
     if (!user.items[type][key] || user.items[type][key] < 0) {
       user.items[type][key] = 0;
     }
-    user.items[type][key] += 1;
+    user.items[type] = {
+      ...user.items[type],
+      [key]: user.items[type][key] + 1,
+    };
     if (user.markModified) user.markModified(`items.${type}`);
   }
 }