diff --git a/lib/postal.when.js b/lib/postal.when.js
index 083e09e..de554ea 100644
--- a/lib/postal.when.js
+++ b/lib/postal.when.js
@@ -62,6 +62,10 @@
             _subscriptions = [];
         };
         _.each(queue, function (sub) {
+            // Add no-op callback for subscriptions with undefined callbacks.
+            if (!sub.callback) {
+                sub.callback = function () {};
+            }
             var subscriptionDefinition = postal.subscribe(sub);
             subscriptionDefinition.data = undefined;
             subscriptionDefinition.subscribe(function (data) {
diff --git a/lib/postal.when.min.js b/lib/postal.when.min.js
index 94fc6e7..a6c41dd 100644
--- a/lib/postal.when.min.js
+++ b/lib/postal.when.min.js
@@ -5,4 +5,4 @@
  * Url: http://github.com/postaljs/postal.when
  * License(s): MIT
  */
-(function(t,n){"object"==typeof module&&module.exports?module.exports=function(t){return n(require("underscore"),t,this)}:"function"==typeof define&&define.amd?define(["underscore","postal"],function(e,o){return n(e,o,t)}):t.postal=n(t._,t.postal,t)})(this,function(t,n,e,o){var i=function(e,i,u,c){var a,r=this,s="[object Function]"===Object.prototype.toString.call(u)?u:function(){},f="[object Object]"===Object.prototype.toString.call(u)?u:c||{},p=[],d=function(){f.timeout&&(a=setTimeout(function(){s({type:"timeout",data:t.pluck(p,"data")})},f.timeout))},l=function(){t.each(p,function(t){t.data=o})},b=function(){var n=t.pluck(p,"data");t.all(n,t.identity)&&(clearTimeout(a),i.apply(this,n),f.once?r.dispose():(l(),d()))};r.dispose=function(){t.each(p,function(t){t.unsubscribe()}),p=[]},t.each(e,function(t){var e=n.subscribe(t);e.data=o,e.subscribe(function(t){e.data=t,b()}),p.push(e)}),d()};return n.when=function(t,n,e,o){return new i(t,n,e,o)},n});
\ No newline at end of file
+(function(t,n){"object"==typeof module&&module.exports?module.exports=function(t){return n(require("underscore"),t,this)}:"function"==typeof define&&define.amd?define(["underscore","postal"],function(e,o){return n(e,o,t)}):t.postal=n(t._,t.postal,t)})(this,function(t,n,e,o){var c=function(e,c,i,u){var a,r=this,f="[object Function]"===Object.prototype.toString.call(i)?i:function(){},s="[object Object]"===Object.prototype.toString.call(i)?i:u||{},l=[],p=function(){s.timeout&&(a=setTimeout(function(){f({type:"timeout",data:t.pluck(l,"data")})},s.timeout))},d=function(){t.each(l,function(t){t.data=o})},b=function(){var n=t.pluck(l,"data");t.all(n,t.identity)&&(clearTimeout(a),c.apply(this,n),s.once?r.dispose():(d(),p()))};r.dispose=function(){t.each(l,function(t){t.unsubscribe()}),l=[]},t.each(e,function(t){t.callback||(t.callback=function(){});var e=n.subscribe(t);e.data=o,e.subscribe(function(t){e.data=t,b()}),l.push(e)}),p()};return n.when=function(t,n,e,o){return new c(t,n,e,o)},n});
\ No newline at end of file
diff --git a/spec/postalwhen.spec.js b/spec/postalwhen.spec.js
index 50e4f87..3049b3f 100755
--- a/spec/postalwhen.spec.js
+++ b/spec/postalwhen.spec.js
@@ -1,9 +1,9 @@
 /* global describe, postal, it, after, before, expect */
 (function(global) {
-    var postal = typeof window === "undefined" ? require("../bower/postal.js/lib/postal.js") : window.postal;
+    var postal = typeof window === "undefined" ? require("postal") : window.postal;
     var expect = typeof window === "undefined" ? require("expect.js") : window.expect;
     var _ = typeof window === "undefined" ? require("underscore") : window._;
-    var postalWhen = typeof window === "undefinde" ? require("../lib/postal.when.js")(postal) : window.postal;
+    var postalWhen = typeof window === "undefined" ? require("../lib/postal.when.js")(postal) : window.postal;
     var subscription;
     var sub;
     var channel;
@@ -182,4 +182,4 @@
 		} );
 	} );
 
-}());
\ No newline at end of file
+}());
diff --git a/src/when.js b/src/when.js
index 94dafa8..7b57093 100755
--- a/src/when.js
+++ b/src/when.js
@@ -41,6 +41,10 @@ var ForkJoin = function ( queue, onSuccess, onError, options ) {
 	};
 
 	_.each( queue, function ( sub ) {
+		// Add no-op callback for subscriptions with undefined callbacks.
+		if (!sub.callback) {
+			sub.callback = function () {};
+		}
 		var subscriptionDefinition = postal.subscribe( sub );
 		subscriptionDefinition.data = undefined;
 		subscriptionDefinition.subscribe( function ( data ) {