diff --git a/lib/webhooks/webhooks.js b/lib/webhooks/webhooks.js
index 7587a8a0bf..d95e96c62b 100644
--- a/lib/webhooks/webhooks.js
+++ b/lib/webhooks/webhooks.js
@@ -47,6 +47,7 @@ function getExpectedBodyHash(body) {
  @returns {boolean} - valid
  */
 function validateRequest(authToken, twilioHeader, url, params) {
+  twilioHeader = twilioHeader || '';
   var expectedSignature = getExpectedTwilioSignature(authToken, url, params);
   return scmp(Buffer.from(twilioHeader), Buffer.from(expectedSignature));
 }
diff --git a/spec/validation.spec.js b/spec/validation.spec.js
index 0863190184..b1a63be2a6 100644
--- a/spec/validation.spec.js
+++ b/spec/validation.spec.js
@@ -69,6 +69,12 @@ describe('Request validation', () => {
 
         expect(isValid).toBeFalsy();
     });
+
+    it('should fail when signature undefined', () => {
+        const isValid = validateRequest(token, undefined, requestUrl, defaultParams);
+
+        expect(isValid).toBeFalsy();
+    });
 });
 
 describe('Request validation middleware', () => {