diff --git a/modules/appnexusBidAdapter.js b/modules/appnexusBidAdapter.js
index c102bee4e58..3a9f37f4ca8 100644
--- a/modules/appnexusBidAdapter.js
+++ b/modules/appnexusBidAdapter.js
@@ -498,6 +498,12 @@ function formatRequest(payload, bidderRequest) {
     }
   }
 
+  if (utils.getParameterByName('apn_test').toUpperCase() === 'TRUE' || config.getConfig('apn_test') === true) {
+    options.customHeaders = {
+      'X-Is-Test': 1
+    }
+  }
+
   if (payload.tags.length > MAX_IMPS_PER_REQUEST) {
     const clonedPayload = utils.deepClone(payload);
 
diff --git a/test/spec/modules/appnexusBidAdapter_spec.js b/test/spec/modules/appnexusBidAdapter_spec.js
index 9b12d892440..a36eab03fe1 100644
--- a/test/spec/modules/appnexusBidAdapter_spec.js
+++ b/test/spec/modules/appnexusBidAdapter_spec.js
@@ -784,6 +784,18 @@ describe('AppNexusAdapter', function () {
       config.getConfig.restore();
     });
 
+    it('should set the X-Is-Test customHeader if test flag is enabled', function () {
+      let bidRequest = Object.assign({}, bidRequests[0]);
+      sinon.stub(config, 'getConfig')
+        .withArgs('apn_test')
+        .returns(true);
+
+      const request = spec.buildRequests([bidRequest]);
+      expect(request.options.customHeaders).to.deep.equal({'X-Is-Test': 1});
+
+      config.getConfig.restore();
+    });
+
     it('should set withCredentials to false if purpose 1 consent is not given', function () {
       let consentString = 'BOJ8RZsOJ8RZsABAB8AAAAAZ+A==';
       let bidderRequest = {