diff --git a/src/FieldsArray.ts b/src/FieldsArray.ts
index f0aa40e..4e95eb9 100644
--- a/src/FieldsArray.ts
+++ b/src/FieldsArray.ts
@@ -1,5 +1,4 @@
 import PKPass from "./PKPass";
-import { fieldKeysPoolSymbol } from "./PKPass";
 import * as Schemas from "./schemas";
 import * as Utils from "./utils";
 import formatMessage, * as Messages from "./messages";
@@ -10,16 +9,20 @@ import formatMessage, * as Messages from "./messages";
  */
 
 const passInstanceSymbol = Symbol("passInstance");
+const sharedKeysPoolSymbol = Symbol("keysPool");
 
 export default class FieldsArray extends Array<Schemas.Field> {
 	private [passInstanceSymbol]: InstanceType<typeof PKPass>;
+	private [sharedKeysPoolSymbol]: Set<string>;
 
 	constructor(
 		passInstance: InstanceType<typeof PKPass>,
+		keysPool: Set<string>,
 		...args: Schemas.Field[]
 	) {
 		super(...args);
 		this[passInstanceSymbol] = passInstance;
+		this[sharedKeysPoolSymbol] = keysPool;
 	}
 
 	/**
@@ -43,9 +46,7 @@ export default class FieldsArray extends Array<Schemas.Field> {
 					return acc;
 				}
 
-				const pool = this[passInstanceSymbol][fieldKeysPoolSymbol];
-
-				if (pool.has(current.key)) {
+				if (this[sharedKeysPoolSymbol].has(current.key)) {
 					console.warn(
 						formatMessage(
 							Messages.FIELDS.REPEATED_KEY,
@@ -55,7 +56,7 @@ export default class FieldsArray extends Array<Schemas.Field> {
 					return acc;
 				}
 
-				pool.add(current.key);
+				this[sharedKeysPoolSymbol].add(current.key);
 				return [...acc, current];
 			},
 			[],
@@ -73,7 +74,7 @@ export default class FieldsArray extends Array<Schemas.Field> {
 		Utils.assertUnfrozen(this[passInstanceSymbol]);
 
 		const element: Schemas.Field = super.pop();
-		this[passInstanceSymbol][fieldKeysPoolSymbol].delete(element.key);
+		this[sharedKeysPoolSymbol].delete(element.key);
 		return element;
 	}
 
@@ -91,7 +92,7 @@ export default class FieldsArray extends Array<Schemas.Field> {
 
 		const removeList = this.slice(start, deleteCount + start);
 		removeList.forEach((item) =>
-			this[passInstanceSymbol][fieldKeysPoolSymbol].delete(item.key),
+			this[sharedKeysPoolSymbol].delete(item.key),
 		);
 
 		return super.splice(start, deleteCount, ...items);
diff --git a/src/PKPass.ts b/src/PKPass.ts
index 7740235..5e5b707 100644
--- a/src/PKPass.ts
+++ b/src/PKPass.ts
@@ -11,7 +11,6 @@ import formatMessage, * as Messages from "./messages";
 /** Exporting for tests specs */
 export const propsSymbol = Symbol("props");
 export const localizationSymbol = Symbol("pass.l10n");
-export const fieldKeysPoolSymbol = Symbol("fieldKeysPoolSymbol");
 export const importMetadataSymbol = Symbol("import.pass.metadata");
 export const createManifestSymbol = Symbol("pass.manifest");
 export const closePassSymbol = Symbol("pass.close");
@@ -20,7 +19,6 @@ export const certificatesSymbol = Symbol("pass.certificates");
 
 export default class PKPass extends Bundle {
 	private [certificatesSymbol]: Schemas.CertificatesSchema;
-	private [fieldKeysPoolSymbol] = new Set<string>();
 	private [propsSymbol]: Schemas.PassProps = {};
 	private [localizationSymbol]: {
 		[lang: string]: {
@@ -310,13 +308,15 @@ export default class PKPass extends Bundle {
 			this[propsSymbol][this.type] = undefined;
 		}
 
+		const sharedKeysPool = new Set<string>();
+
 		this[passTypeSymbol] = type;
 		this[propsSymbol][this[passTypeSymbol]] = {
-			headerFields /******/: new FieldsArray(this),
-			primaryFields /*****/: new FieldsArray(this),
-			secondaryFields /***/: new FieldsArray(this),
-			auxiliaryFields /***/: new FieldsArray(this),
-			backFields /********/: new FieldsArray(this),
+			headerFields /******/: new FieldsArray(this, sharedKeysPool),
+			primaryFields /*****/: new FieldsArray(this, sharedKeysPool),
+			secondaryFields /***/: new FieldsArray(this, sharedKeysPool),
+			auxiliaryFields /***/: new FieldsArray(this, sharedKeysPool),
+			backFields /********/: new FieldsArray(this, sharedKeysPool),
 			transitType: undefined,
 		};
 	}