diff --git a/lib/utils.js b/lib/utils.js
index 2bec38a..7dd6f0a 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -4,6 +4,9 @@ import pkgJson from '../package.json'
 const Promise = window.Promise || NativePromise
 
 export function updateUserAgentWithAppId (headers, appId) {
+  if (!appId) {
+    return headers
+  }
   const originalUserAgent = headers && headers['User-Agent'] ? headers['User-Agent'] : ''
   const zafSdkUserAgentString = `zendesk_app_framework_sdk/sdk_version:${pkgJson.version}/app_id:${appId}`
   const userAgent = originalUserAgent ? `${originalUserAgent} ${zafSdkUserAgentString}` : zafSdkUserAgentString
diff --git a/spec/utils_spec.js b/spec/utils_spec.js
index 033fca1..cc0bb5f 100644
--- a/spec/utils_spec.js
+++ b/spec/utils_spec.js
@@ -159,12 +159,51 @@ describe('Utils', () => {
       global.pkgJson = { version: '1.0.0' }
     })
 
-    it('should append the app id to the user agent', () => {
-      const headers = { 'User-Agent': 'Mozilla/5.0' }
-      const appId = '1'
-      const updatedHeaders = Utils.updateUserAgentWithAppId(headers, appId)
-      const expectedUserAgent = `Mozilla/5.0 zendesk_app_framework_sdk/sdk_version:${pkgJson.version}/app_id:${appId}`
-      expect(updatedHeaders['User-Agent']).to.equal(expectedUserAgent)
+    describe('with a valid app id', () => {
+      let appId
+
+      beforeEach(() => {
+        appId = '1'
+      })
+      
+      it('should append the app id to the user agent', () => {
+        const headers = { 'User-Agent': 'Mozilla/5.0' }
+        const updatedHeaders = Utils.updateUserAgentWithAppId(headers, appId)
+        const expectedUserAgent = `Mozilla/5.0 zendesk_app_framework_sdk/sdk_version:${pkgJson.version}/app_id:${appId}`
+        expect(updatedHeaders['User-Agent']).to.equal(expectedUserAgent)
+      })
+
+      it('should handle an undefined headers object', () => {
+        const updatedHeaders = Utils.updateUserAgentWithAppId(undefined, appId)
+        const expectedUserAgent = `zendesk_app_framework_sdk/sdk_version:${pkgJson.version}/app_id:${appId}`
+        expect(updatedHeaders['User-Agent']).to.equal(expectedUserAgent)
+      })
+
+      it('should handle a headers object with no User-Agent', () => {
+        const headers = {}
+        const updatedHeaders = Utils.updateUserAgentWithAppId(headers, appId)
+        const expectedUserAgent = `zendesk_app_framework_sdk/sdk_version:${pkgJson.version}/app_id:${appId}`
+        expect(updatedHeaders['User-Agent']).to.equal(expectedUserAgent)
+      })
+    })
+
+    describe('with an undefined app id', () => {
+      it('should not append the app id to the user agent', () => {
+        const headers = { 'User-Agent': 'Mozilla/5.0' }
+        const updatedHeaders = Utils.updateUserAgentWithAppId(headers)
+        expect(updatedHeaders['User-Agent']).to.equal('Mozilla/5.0')
+      })
+
+      it('should handle an undefined headers object', () => {
+        const updatedHeaders = Utils.updateUserAgentWithAppId()
+        expect(updatedHeaders).to.be.undefined()
+      })
+
+      it('should handle a headers object with no User-Agent', () => {
+        const headers = {}
+        const updatedHeaders = Utils.updateUserAgentWithAppId(headers)
+        expect(updatedHeaders['User-Agent']).to.equal(undefined)
+      })
     })
   })
 })