diff --git a/knockout-sortable.js b/knockout-sortable.js
index dac7f6f..dcb470a 100644
--- a/knockout-sortable.js
+++ b/knockout-sortable.js
@@ -1,16 +1,54 @@
 (function (factory) {
     "use strict";
-    if (typeof define === "function" && define.amd) {
-        // AMD anonymous module
-        define(["knockout", "./Sortable"], factory);
-    } else if (typeof require === "function" && typeof exports === "object" && typeof module === "object") {
-        // CommonJS module
-        var ko = require("knockout");
-        var Sortable = require('./Sortable');
-        factory(ko, Sortable);
-    } else {
-        // No module loader (plain <script> tag) - put directly in global namespace
-        factory(window.ko, window.Sortable);
+    //get ko ref via global or require
+    var koRef;
+    if (typeof ko !== 'undefined') {
+      //global ref already defined
+      koRef = ko;
+    }
+    else if (typeof require === 'function' && typeof exports === 'object' && typeof module === 'object') {
+      //commonjs / node.js
+      koRef = require('knockout');
+    }
+    //get sortable ref via global or require
+    var sortableRef;
+    if (typeof Sortable !== 'undefined') {
+      //global ref already defined
+      sortableRef = Sortable;
+    }
+    else if (typeof require === 'function' && typeof exports === 'object' && typeof module === 'object') {
+      //commonjs / node.js
+      sortableRef = require('sortablejs');
+    }
+    //use references if we found them
+    if (koRef !== undefined && sortableRef !== undefined) {
+      factory(koRef, sortableRef);
+    }
+    //if both references aren't found yet, get via AMD if available
+    else if (typeof define === 'function' && define.amd){
+      //we may have a reference to only 1, or none
+      if (koRef !== undefined && sortableRef === undefined) {
+        define(['./Sortable'], function(amdSortableRef){ factory(koRef, amdSortableRef); });
+      }
+      else if (koRef === undefined && sortableRef !== undefined) {
+        define(['knockout'], function(amdKnockout){ factory(amdKnockout, sortableRef); });
+      }
+      else if (koRef === undefined && sortableRef === undefined) {
+        define(['knockout', './Sortable'], factory);
+      }
+    }
+    //no more routes to get references
+    else {
+      //report specific error
+      if (koRef !== undefined && sortableRef === undefined) {
+        throw new Error('knockout-sortable could not get reference to Sortable');
+      }
+      else if (koRef === undefined && sortableRef !== undefined) {
+        throw new Error('knockout-sortable could not get reference to Knockout');
+      }
+      else if (koRef === undefined && sortableRef === undefined) {
+        throw new Error('knockout-sortable could not get reference to Knockout or Sortable');
+      }
     }
 })(function (ko, Sortable) {
     "use strict";