diff --git a/event_processor.js b/event_processor.js
index 89e8951..a67a4ac 100644
--- a/event_processor.js
+++ b/event_processor.js
@@ -1,5 +1,6 @@
 const LRUCache = require('lrucache');
 const request = require('request');
+const uuidv4 = require('uuid/v4');
 const EventSummarizer = require('./event_summarizer');
 const UserFilter = require('./user_filter');
 const errors = require('./errors');
@@ -188,16 +189,16 @@ function EventProcessor(sdkKey, config, errorReporter) {
 
       config.logger.debug('Flushing %d events', worklist.length);
 
-      tryPostingEvents(worklist, resolve, reject, true);
+      tryPostingEvents(worklist, uuidv4(), resolve, reject, true);
     }), callback);
   };
 
-  function tryPostingEvents(events, resolve, reject, canRetry) {
+  function tryPostingEvents(events, payloadId, resolve, reject, canRetry) {
     const retryOrReject = err => {
       if (canRetry) {
         config.logger && config.logger.warn('Will retry posting events after 1 second');
         setTimeout(() => {
-          tryPostingEvents(events, resolve, reject, false);
+          tryPostingEvents(events, payloadId, resolve, reject, false);
         }, 1000);
       } else {
         reject(err);
@@ -210,7 +211,8 @@ function EventProcessor(sdkKey, config, errorReporter) {
       headers: {
         'Authorization': sdkKey,
         'User-Agent': config.userAgent,
-        'X-LaunchDarkly-Event-Schema': '3'
+        'X-LaunchDarkly-Event-Schema': '3',
+        'X-LaunchDarkly-Payload-ID': payloadId
       },
       json: true,
       body: events,
diff --git a/package-lock.json b/package-lock.json
index 9e13c64..e8480ae 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -7496,9 +7496,9 @@
       }
     },
     "uuid": {
-      "version": "3.3.2",
-      "resolved": "https://registry.npmjs.org/uuid/-/uuid-3.3.2.tgz",
-      "integrity": "sha512-yXJmeNaw3DnnKAOKJE51sL/ZaYfWJRl1pK9dr19YFCu0ObS231AB1/LbqTKRAQ5kw8A90rA6fr4riOUpTZvQZA=="
+      "version": "3.3.3",
+      "resolved": "https://registry.npmjs.org/uuid/-/uuid-3.3.3.tgz",
+      "integrity": "sha512-pW0No1RGHgzlpHJO1nsVrHKpOEIxkGg1xB+v0ZmdNH5OAeAwzAVrCnI2/6Mtx+Uys6iaylxa+D3g4j63IKKjSQ=="
     },
     "v8-compile-cache": {
       "version": "2.1.0",
diff --git a/package.json b/package.json
index a258891..1396c04 100644
--- a/package.json
+++ b/package.json
@@ -34,6 +34,7 @@
     "request-etag": "^2.0.3",
     "semver": "^6.3.0",
     "tunnel": "0.0.6",
+    "uuid": "^3.3.3",
     "winston": "2.4.1",
     "yaml": "1.0.1"
   },
diff --git a/test.js b/test.js
deleted file mode 100644
index d5764f7..0000000
--- a/test.js
+++ /dev/null
@@ -1,32 +0,0 @@
-var ld = require('./index.js');
-var winston = require('winston');
-
-var logger = new winston.Logger({
-level: 'debug',
-transports: [
-  new (winston.transports.Console)(({
-    formatter: function(options) {
-      return '[LaunchDarkly] ' + (options.message ? options.message : '');
-    }
-  })),
-]
-});
-
-var fileSource = ld.FileDataSource({ paths: [ 'test.yml' ], autoUpdate: true, logger: logger });
-
-var config = {
-	baseUri: 'https://ld-stg.launchdarkly.com',
-	streamUri: 'https://stream-stg.launchdarkly.com',
-	eventsUri: 'https://events-stg.launchdarkly.com',
-	sendEvents: false,
-	//updateProcessor: fileSource,
-	logger: logger
-};
-
-var client = ld.init('sdk-0acc1044-9cf7-40ea-919f-7b5a8540d9d8', config);
-
-client.on('ready', function() {
-	client.variation('catflag', {key: 'user'}, 'bear', function(err, value) {
-		console.log('catflag: ' + value);
-	});
-});
diff --git a/test/event_processor-test.js b/test/event_processor-test.js
index 2745301..9e1f70d 100644
--- a/test/event_processor-test.js
+++ b/test/event_processor-test.js
@@ -483,6 +483,24 @@ describe('EventProcessor', () => {
     });
   }));
 
+  it('sends unique payload IDs', eventsServerTest(async s => {
+    await withEventProcessor(defaultConfig, s, async ep => {
+      const e = { kind: 'identify', creationDate: 1000, user: user };
+      ep.sendEvent(e);
+      await ep.flush();
+      ep.sendEvent(e);
+      await ep.flush();
+
+      const req0 = await s.nextRequest();
+      const req1 = await s.nextRequest();
+      const id0 = req0.headers['x-launchdarkly-payload-id'];
+      const id1 = req1.headers['x-launchdarkly-payload-id'];
+      expect(id0).toBeTruthy();
+      expect(id1).toBeTruthy();
+      expect(id0).not.toEqual(id1);
+    });
+  }));
+
   function verifyUnrecoverableHttpError(status) {
     return eventsServerTest(async s => {
       s.forMethodAndPath('post', '/bulk', TestHttpHandlers.respond(status));
@@ -510,13 +528,18 @@ describe('EventProcessor', () => {
         await expect(ep.flush()).rejects.toThrow('error ' + status);
 
         expect(s.requestCount()).toEqual(2);
-        await s.nextRequest();
-        await s.nextRequest();
+        const req0 = await s.nextRequest();
+        const req1 = await s.nextRequest();
+        expect(req0.body).toEqual(req1.body);
+        const id0 = req0.headers['x-launchdarkly-payload-id'];
+        expect(req1.headers['x-launchdarkly-payload-id']).toEqual(id0);
 
         s.forMethodAndPath('post', '/bulk', TestHttpHandlers.respond(200));
         ep.sendEvent(e);
         await ep.flush();
         expect(s.requestCount()).toEqual(3);
+        const req2 = await s.nextRequest();
+        expect(req2.headers['x-launchdarkly-payload-id']).not.toEqual(id0);
       });
     });
   }