diff --git a/lib/worker.js b/lib/worker.js
index <HASH>..<HASH> 100644
--- a/lib/worker.js
+++ b/lib/worker.js
@@ -112,7 +112,7 @@ worker.prototype.poll = function(nQueue, callback){
             self.result = null;
             self.perform(currentJob);
           }else{
-            callback(currentJob);
+            if(typeof callback === 'function'){ callback(currentJob); }
           }
         }else{
           if(error){
@@ -124,7 +124,7 @@ worker.prototype.poll = function(nQueue, callback){
               if(self.options.looping){
                 self.pause();
               }else{
-                callback();
+                if(typeof callback === 'function'){ callback(); }
               }
             });
           }else{
worker poll callbacks only if callback is defined