diff --git a/src/__tests__/posthog-core.js b/src/__tests__/posthog-core.js
index f879a180a..e3bb3a920 100644
--- a/src/__tests__/posthog-core.js
+++ b/src/__tests__/posthog-core.js
@@ -14,6 +14,8 @@ jest.mock('../gdpr-utils', () => ({
 }))
 jest.mock('../decide')
 
+jest.useFakeTimers().setSystemTime(new Date('2020-01-01'))
+
 given('lib', () => {
     const posthog = new PostHog()
     posthog._init('testtoken', given.config, 'testhog')
@@ -74,6 +76,22 @@ describe('posthog core', () => {
             expect(captureData).toHaveProperty('uuid')
         })
 
+        it('adds system time to events', () => {
+            const captureData = given.subject()
+            expect(captureData).toHaveProperty('timestamp')
+            // timer is fixed at 2020-01-01
+            expect(captureData.timestamp).toEqual(new Date(2020, 0, 1))
+        })
+
+        it('captures when time is overriden by caller', () => {
+            given.options = { timestamp: new Date(2020, 0, 2, 12, 34) }
+            const captureData = given.subject()
+            expect(captureData).toHaveProperty('timestamp')
+            expect(captureData.timestamp).toEqual(new Date(2020, 0, 2, 12, 34))
+            expect(captureData.properties['$event_time_override_provided']).toEqual(true)
+            expect(captureData.properties['$event_time_override_system_time']).toEqual(new Date(2020, 0, 1))
+        })
+
         it('handles recursive objects', () => {
             given('eventProperties', () => {
                 const props = {}
diff --git a/src/posthog-core.ts b/src/posthog-core.ts
index eba796d3b..28cb74f04 100644
--- a/src/posthog-core.ts
+++ b/src/posthog-core.ts
@@ -921,6 +921,10 @@ export class PostHog {
 
         data = _copyAndTruncateStrings(data, options._noTruncate ? null : this.config.properties_string_max_length)
         data.timestamp = options.timestamp || new Date()
+        if (!_isUndefined(options.timestamp)) {
+            data.properties['$event_time_override_provided'] = true
+            data.properties['$event_time_override_system_time'] = new Date()
+        }
 
         // Top-level $set overriding values from the one from properties is taken from the plugin-server normalizeEvent
         // This doesn't handle $set_once, because posthog-people doesn't either