diff --git a/fvtt-celestopol.mjs b/fvtt-celestopol.mjs
index b0645c8..1e136af 100644
--- a/fvtt-celestopol.mjs
+++ b/fvtt-celestopol.mjs
@@ -74,7 +74,7 @@ Hooks.once("init", () => {
     label: "CELESTOPOL.Sheet.npc",
   })
 
-  foundry.documents.collections.Items.unregisterSheet("core", ItemSheet)
+  foundry.documents.collections.Items.unregisterSheet("core", foundry.appv1.sheets.ItemSheet)
   foundry.documents.collections.Items.registerSheet(SYSTEM_ID, CelestopolAnomalySheet, {
     types: ["anomaly"],
     makeDefault: true,