diff --git a/src/helpers.js b/src/helpers.js
index 1d4b59cab..a96dcf5ad 100644
--- a/src/helpers.js
+++ b/src/helpers.js
@@ -1,11 +1,5 @@
 // Helper functions used internally across the library
 
-const utils = require('./utils');
-const javaZDT = Java.type('java.time.ZonedDateTime');
-const javaDuration = Java.type('java.time.Duration');
-const javaInstant = Java.type('java.time.Instant');
-const javaTimeSeries = Java.type('org.openhab.core.types.TimeSeries');
-
 /**
  * @typedef { import("./items/items").Item } Item
  * @private
@@ -53,7 +47,7 @@ function _toOpenhabPrimitiveType (value) {
  * Checks whether the given object is an instance of {@link items.Item}.
  *
  * To be used when instanceof checks don't work because of circular dependencies or webpack compilation.
- * Checks constructor name or unique properties, because constructor name does not work for the webpacked globals injection.
+ * Checks unique property <code>rawItem</code>, because constructor name does not work for the webpacked globals injection.
  *
  * @param {*} o
  * @returns {boolean}
@@ -61,14 +55,14 @@ function _toOpenhabPrimitiveType (value) {
  */
 function _isItem (o) {
   if (typeof o !== 'object') return false;
-  return ((o.constructor && o.constructor.name === 'Item') || typeof o.rawItem === 'object');
+  return typeof o.rawItem === 'object';
 }
 
 /**
  * Checks whether the given object is an instance of {@link Quantity}.
  *
  * To be used when instanceof checks don't work because of circular dependencies or webpack compilation.
- * Checks constructor name or unique properties, because constructor name does not work for the webpacked globals injection.
+ * Checks unique property <code>rawQtyType</code>, because constructor name does not work for the webpacked globals injection.
  *
  * @param {*} o
  * @returns {boolean}
@@ -76,14 +70,14 @@ function _isItem (o) {
  */
 function _isQuantity (o) {
   if (typeof o !== 'object') return false;
-  return ((o.constructor && o.constructor.name === 'Quantity') || typeof o.rawQtyType === 'object');
+  return typeof o.rawQtyType === 'object';
 }
 
 /**
  * Checks whether the given object is an instance of {@link time.ZonedDateTime}.
  *
  * To be used when instanceof checks don't work because of circular dependencies or webpack compilation.
- * Checks constructor name or unique properties, because constructor name does not work for the webpacked globals injection.
+ * Checks <code>_isZonedDateTime</code> property, because constructor name does not work for the webpacked globals injection.
  *
  * @param {*} o
  * @returns {boolean}
@@ -91,16 +85,14 @@ function _isQuantity (o) {
  */
 function _isZonedDateTime (o) {
   if (typeof o !== 'object') return false;
-  return (((o.constructor && o.constructor.name === 'ZonedDateTime')) ||
-    (!utils.isJsInstanceOfJavaType(o, javaZDT) && typeof o.withFixedOffsetZone === 'function')
-  );
+  return o._isZonedDateTime === true;
 }
 
 /**
  * Checks whether the given object is an instance of {@link time.Duration}.
  *
  * To be used when instanceof checks don't work because of circular dependencies or webpack compilation.
- * Checks constructor name or unique properties, because constructor name does not work for the webpacked globals injection.
+ * Checks <code>_isDuration</code> property, because constructor name does not work for the webpacked globals injection.
  *
  * @param {*} o
  * @returns {boolean}
@@ -108,16 +100,14 @@ function _isZonedDateTime (o) {
  */
 function _isDuration (o) {
   if (typeof o !== 'object') return false;
-  return (((o.constructor && o.constructor.name === 'Duration')) ||
-    (!utils.isJsInstanceOfJavaType(o, javaDuration) && typeof o.minusDuration === 'function' && typeof o.toNanos === 'function')
-  );
+  return o._isDuration === true;
 }
 
 /**
  * Checks whether the given object is an instance of {@link time.Instant}.
  *
  * To be used when instanceof checks don't work because of circular dependencies or webpack compilation.
- * Checks constructor name or unique properties, because constructor name does not work for the webpacked globals injection
+ * Checks <code>_isInstant</code> property, because constructor name does not work for the webpacked globals injection.
  *
  * @param {*} o
  * @returns {boolean}
@@ -125,16 +115,14 @@ function _isDuration (o) {
  */
 function _isInstant (o) {
   if (typeof o !== 'object') return false;
-  return (((o.constructor && o.constructor.name === 'Instant')) ||
-    (!utils.isJsInstanceOfJavaType(o, javaInstant) && typeof o.policy === 'string' && typeof o.ofEpochMicro === 'function' && typeof o.ofEpochMilli === 'function' && o.ofEpochSecond === 'function')
-  );
+  return o._isInstant === true;
 }
 
 /**
  * Checks whether the given object is an instance of {@link items.TimeSeries}.
  *
  * To be used when instanceof checks don't work because of circular dependencies or webpack compilation.
- * Checks constructor name or unique properties, because constructor name does not work for the webpacked globals injection.
+ * Checks <code>_isTimeSeries</code> property, because constructor name does not work for the webpacked globals injection.
  *
  * @param {*} o
  * @return {boolean}
@@ -142,9 +130,7 @@ function _isInstant (o) {
  */
 function _isTimeSeries (o) {
   if (typeof o !== 'object') return false;
-  return (((o.constructor && o.constructor.name === 'TimeSeries')) ||
-    (!utils.isJsInstanceOfJavaType(o, javaTimeSeries) && _isInstant(o.begin) && _isInstant(o.end))
-  );
+  return o._isTimeSeries === true;
 }
 
 module.exports = {
diff --git a/src/items/time-series.js b/src/items/time-series.js
index 9713c6330..ed58aae60 100644
--- a/src/items/time-series.js
+++ b/src/items/time-series.js
@@ -21,6 +21,11 @@ const { _isInstant } = require('../helpers');
  * @memberof items
  */
 class TimeSeries {
+  /**
+   * @type {boolean}
+   * @private
+   */
+  _isTimeSeries = true;
   #states = [];
   #policy;
 
diff --git a/src/time.js b/src/time.js
index fe2f5bd91..7dbe8dd1c 100644
--- a/src/time.js
+++ b/src/time.js
@@ -454,9 +454,14 @@ time.ZonedDateTime.prototype.toOpenHabString = function () {
   return this.toString().replace(/\[[^\]]*]$/, '');
 };
 
+// Add fields to allow identification of the object type
+time.ZonedDateTime.prototype._isZonedDateTime = true;
+time.Duration.prototype._isDuration = true;
+time.Instant.prototype._isInstant = true;
+
 module.exports = {
   ...time,
   toZDT,
-  parseString: _parseString,
-  parseISO8601: _parseISO8601
+  _parseString,
+  _parseISO8601
 };
diff --git a/test/quantity.spec.js b/test/quantity.spec.js
index 1d9872b81..d37d0df01 100644
--- a/test/quantity.spec.js
+++ b/test/quantity.spec.js
@@ -5,6 +5,7 @@ const { getQuantity, Quantity, QuantityError, _toBigDecimalOrQtyType, _toQtyType
 
 class Item {
   constructor (rawState) {
+    this.rawItem = {}; // required for _isItem
     this.rawState = rawState;
   }
 }
diff --git a/test/time.spec.js b/test/time.spec.js
index b16789df1..e8f2eb867 100644
--- a/test/time.spec.js
+++ b/test/time.spec.js
@@ -25,7 +25,7 @@ describe('time.js', () => {
   });
 
   describe('parseString', () => {
-    const parseString = time.parseString;
+    const parseString = time._parseString;
 
     describe('accepts ISO patterns without the "T" for Blockly', () => {
       it.each([
@@ -42,7 +42,7 @@ describe('time.js', () => {
   });
 
   describe('parseISO8601', () => {
-    const parseISO8601 = time.parseISO8601;
+    const parseISO8601 = time._parseISO8601;
     const ZonedDateTime = require('@js-joda/core').ZonedDateTime;
 
     describe('parses ISO Date', () => {
diff --git a/types/items/time-series.d.ts b/types/items/time-series.d.ts
index f51228628..f4d055036 100644
--- a/types/items/time-series.d.ts
+++ b/types/items/time-series.d.ts
@@ -28,6 +28,11 @@ declare class TimeSeries {
      * @param {string} policy TimeSeries policy <code>ADD</code> or <code>REPLACE</code>
      */
     constructor(policy: string);
+    /**
+     * @type {boolean}
+     * @private
+     */
+    private _isTimeSeries;
     /**
      * The persistence policy of this TimeSeries
      *
diff --git a/types/items/time-series.d.ts.map b/types/items/time-series.d.ts.map
index ddf31fc16..e013fac96 100644
--- a/types/items/time-series.d.ts.map
+++ b/types/items/time-series.d.ts.map
@@ -1 +1 @@
-{"version":3,"file":"time-series.d.ts","sourceRoot":"","sources":["../../src/items/time-series.js"],"names":[],"mappings":";AAGA;;;GAGG;AACH;;;GAGG;AACH;;;GAGG;AAEH;;;;;GAKG;AACH;IAIE;;;;;;;;OAQG;IACH,oBAFW,MAAM,EAKhB;IAED;;;;OAIG;IACH,qBAEC;IAED;;;OAGG;IACH,4BAEC;IAED;;;OAGG;IACH,0BAEC;IAED;;;OAGG;IACH,mBAEC;IAED;;;;;;OAMG;IACH,oBAEC;IAED;;;;;;;;OAQG;IACH,eAJW,CAAC,KAAK,OAAO,GAAC,KAAK,aAAa,GAAC,MAAM,GAAC,IAAI,CAAC,SAC7C,MAAM,GAAC,MAAM,GAAC,QAAQ,YAAU,GAC9B,UAAU,CAMtB;IAED,mBAOC;;CACF;;;;;mBAvGa,OAAO,eAAe,EAAE,OAAO;yBAI/B,OAAO,eAAe,EAAE,aAAa;;;gBAItC,OAAO,aAAa,EAAE,QAAQ"}
\ No newline at end of file
+{"version":3,"file":"time-series.d.ts","sourceRoot":"","sources":["../../src/items/time-series.js"],"names":[],"mappings":";AAGA;;;GAGG;AACH;;;GAGG;AACH;;;GAGG;AAEH;;;;;GAKG;AACH;IASE;;;;;;;;OAQG;IACH,oBAFW,MAAM,EAKhB;IApBD;;;OAGG;IACH,sBAAqB;IAkBrB;;;;OAIG;IACH,qBAEC;IAED;;;OAGG;IACH,4BAEC;IAED;;;OAGG;IACH,0BAEC;IAED;;;OAGG;IACH,mBAEC;IAED;;;;;;OAMG;IACH,oBAEC;IAED;;;;;;;;OAQG;IACH,eAJW,CAAC,KAAK,OAAO,GAAC,KAAK,aAAa,GAAC,MAAM,GAAC,IAAI,CAAC,SAC7C,MAAM,GAAC,MAAM,GAAC,QAAQ,YAAU,GAC9B,UAAU,CAMtB;IAED,mBAOC;;CACF;;;;;mBA5Ga,OAAO,eAAe,EAAE,OAAO;yBAI/B,OAAO,eAAe,EAAE,aAAa;;;gBAItC,OAAO,aAAa,EAAE,QAAQ"}
\ No newline at end of file
diff --git a/types/time.d.ts b/types/time.d.ts
index a5d583a90..90e73ea4f 100644
--- a/types/time.d.ts
+++ b/types/time.d.ts
@@ -1,7 +1,7 @@
 declare const _exports: {
     toZDT: typeof toZDT;
-    parseString: typeof _parseString;
-    parseISO8601: typeof _parseISO8601;
+    _parseString: typeof _parseString;
+    _parseISO8601: typeof _parseISO8601;
     nativeJs(date: any, zone?: time.ZoneId): time.ZonedDateTime;
     convert(temporal: time.LocalDate | time.Instant | time.ZonedDateTime | time.LocalDateTime, zone?: time.ZoneId): {
         toDate: () => Date;