diff --git a/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/common/normalizers.ts b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/common/normalizers.ts
index 1d329a598f623b..243875cd1de2a8 100644
--- a/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/common/normalizers.ts
+++ b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/common/normalizers.ts
@@ -6,6 +6,7 @@
  */
 
 import { NewPackagePolicyInput } from '@kbn/fleet-plugin/common';
+import { parseJsonIfString } from '../helpers/parsers';
 import { CommonFields, ConfigKey, DataStream } from '../types';
 import {
   DEFAULT_COMMON_FIELDS,
@@ -27,7 +28,8 @@ export type CommonNormalizerMap = Record<keyof CommonFields | ConfigKey.NAME, No
 export const cronToSecondsNormalizer = (value: string) =>
   value ? value.slice(0, value.length - 1) : null;
 
-export const jsonToJavascriptNormalizer = (value: string) => (value ? JSON.parse(value) : null);
+export const jsonToJavascriptNormalizer = (value: string) =>
+  value ? parseJsonIfString(value) : null;
 
 export function getNormalizer<Fields>(key: string, defaultValues: Fields): Normalizer {
   return (fields: NewPackagePolicyInput['vars']) =>
diff --git a/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/helpers/parsers.ts b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/helpers/parsers.ts
new file mode 100644
index 00000000000000..7dcba327386e62
--- /dev/null
+++ b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/helpers/parsers.ts
@@ -0,0 +1,14 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+export function parseJsonIfString<T>(value: T) {
+  if (typeof value === 'string') {
+    return JSON.parse(value);
+  }
+
+  return value;
+}
diff --git a/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/http/normalizers.ts b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/http/normalizers.ts
index a4013a0e8024db..f7e7ad3eeac2ee 100644
--- a/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/http/normalizers.ts
+++ b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/http/normalizers.ts
@@ -5,6 +5,7 @@
  * 2.0.
  */
 
+import { parseJsonIfString } from '../helpers/parsers';
 import { HTTPFields, ConfigKey, ContentType, contentTypesToMode } from '../types';
 import {
   Normalizer,
@@ -56,7 +57,7 @@ export const httpNormalizers: HTTPNormalizerMap = {
     const requestHeaders = fields?.[ConfigKey.REQUEST_HEADERS_CHECK]?.value;
     if (requestBody) {
       const headers = requestHeaders
-        ? JSON.parse(fields?.[ConfigKey.REQUEST_HEADERS_CHECK]?.value)
+        ? parseJsonIfString(fields?.[ConfigKey.REQUEST_HEADERS_CHECK]?.value)
         : defaultHTTPAdvancedFields[ConfigKey.REQUEST_HEADERS_CHECK];
       const requestBodyValue =
         requestBody !== null && requestBody !== undefined
diff --git a/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/tls/normalizers.ts b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/tls/normalizers.ts
index a4cf9f280e9a72..eb52494d2cb961 100644
--- a/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/tls/normalizers.ts
+++ b/x-pack/plugins/synthetics/public/legacy_uptime/components/fleet_package/tls/normalizers.ts
@@ -5,6 +5,7 @@
  * 2.0.
  */
 
+import { parseJsonIfString } from '../helpers/parsers';
 import { TLSFields, ConfigKey } from '../types';
 import { Normalizer } from '../common/normalizers';
 import { defaultTLSFields } from '../contexts';
@@ -41,4 +42,4 @@ export const tlsNormalizers: TLSNormalizerMap = {
 export const tlsStringToObjectNormalizer = (value: string = '', key: keyof TLSFields) =>
   value ?? defaultTLSFields[key];
 export const tlsJsonToObjectNormalizer = (value: string = '', key: keyof TLSFields) =>
-  value ? JSON.parse(value) : defaultTLSFields[key];
+  value ? parseJsonIfString(value) : defaultTLSFields[key];