diff --git a/index.js b/index.js
index 37dd0c5..6b0be78 100644
--- a/index.js
+++ b/index.js
@@ -107,8 +107,9 @@ module.exports.verify = function(jwtString, secretOrPublicKey, options, callback
     return done(new JsonWebTokenError('jwt signature is required'));
   }
 
-  if (typeof secretOrPublicKey === "undefined" || secretOrPublicKey === null) // secretOrPublicKey can be empty string
+  if (!secretOrPublicKey) {
     return done(new JsonWebTokenError('secret or public key must be provided'));
+  }
 
   if (!options.algorithms) {
     options.algorithms = ~secretOrPublicKey.toString().indexOf('BEGIN CERTIFICATE') ||