diff --git a/specs/PKPass.spec.cjs b/specs/PKPass.spec.cjs
index beb8881..845360d 100644
--- a/specs/PKPass.spec.cjs
+++ b/specs/PKPass.spec.cjs
@@ -712,12 +712,12 @@ describe("PKPass", () => {
 
 	describe("expiration date", () => {
 		it("should set a pass expiration date", () => {
-			pkpass.setExpirationDate(new Date(2023, 3, 10));
+			pkpass.setExpirationDate(new Date("2023-04-09T17:00-07:00"));
 
 			const passjsonGenerated = getGeneratedPassJson(pkpass);
 
 			expect(passjsonGenerated.expirationDate).toBe(
-				"2023-04-10T00:00:00Z",
+				"2023-04-10T00:00:00.000Z",
 			);
 		});
 
@@ -808,11 +808,11 @@ describe("PKPass", () => {
 
 	describe("relevant date", () => {
 		it("should set pass relevant date", () => {
-			pkpass.setRelevantDate(new Date(2023, 3, 10, 14, 15));
+			pkpass.setRelevantDate(new Date("2023-04-11T00:15+10:00"));
 
 			const passjsonGenerated = getGeneratedPassJson(pkpass);
 
-			expect(passjsonGenerated.relevantDate).toBe("2023-04-10T14:15:00Z");
+			expect(passjsonGenerated.relevantDate).toBe("2023-04-10T14:15:00.000Z");
 		});
 
 		it("should reset relevant date", () => {
diff --git a/specs/utils.spec.cjs b/specs/utils.spec.cjs
index 3636dd0..9a5ad3e 100644
--- a/specs/utils.spec.cjs
+++ b/specs/utils.spec.cjs
@@ -32,8 +32,8 @@ describe("Utils", () => {
 		});
 
 		it("should convert a Date object to a valid W3C date", () => {
-			expect(processDate(new Date(2020, 6, 1, 0, 0, 0, 0))).toBe(
-				"2020-07-01T00:00:00Z",
+			expect(processDate(new Date("2020-07-01T02:00+02:00"))).toBe(
+				"2020-07-01T00:00:00.000Z",
 			);
 		});
 	});
diff --git a/src/utils.ts b/src/utils.ts
index 2ce999f..a0110e6 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -36,34 +36,11 @@ function dateToW3CString(date: Date) {
 		return undefined;
 	}
 
-	const paddedMonth = padMeTwo(date.getMonth() + 1);
-	const paddedDay = padMeTwo(date.getDate());
-	const paddedHour = padMeTwo(date.getHours());
-	const paddedMinutes = padMeTwo(date.getMinutes());
-	const paddedSeconds = padMeTwo(date.getSeconds());
-
 	/**
-	 * Date.prototype.getTimezoneOffset returns the timezone UTC offset in
-	 * minutes of the local machine.
-	 *
-	 * That value should then be used to calculate the effective timezone as
-	 * string, but still that would be related to the machine and not to the
-	 * specified date.
-	 *
-	 * For this reason we are completing date with "Z" TimeZoneDesignator (TZD)
-	 * to say it to use local timezone.
-	 *
-	 * In the future we might think to integrate another parameter to represent
-	 * a custom timezone.
-	 *
 	 * @see https://www.w3.org/TR/NOTE-datetime
 	 */
 
-	return `${date.getFullYear()}-${paddedMonth}-${paddedDay}T${paddedHour}:${paddedMinutes}:${paddedSeconds}Z`;
-}
-
-function padMeTwo(original: string | number) {
-	return String(original).padStart(2, "0");
+	return date.toISOString();
 }
 
 /**