diff --git a/index.html b/index.html
index 59cae8491..f46a6b9a5 100644
--- a/index.html
+++ b/index.html
@@ -111,11 +111,11 @@ <h2>Downloads <i style="padding-left: 12px; font-size:12px;">(Right-click, and u
     <p>
       <table>
         <tr>
-          <td><a href="underscore.js">Development Version (1.0.0)</a></td>
+          <td><a href="underscore.js">Development Version (1.0.1)</a></td>
           <td><i>25kb, Uncompressed with Comments</i></td>
         </tr>
         <tr>
-          <td><a href="underscore-min.js">Production Version (1.0.0)</a></td>
+          <td><a href="underscore-min.js">Production Version (1.0.1)</a></td>
           <td><i>2.5kb, Packed and Gzipped</i></td>
         </tr>
       </table>
@@ -1136,6 +1136,12 @@ <h2>Links &amp; Suggested Reading</h2>
 
       <h2>Change Log</h2>
       
+      <p>
+        <b class="header">1.0.1</b><br />
+        Bugfix for <tt>_.isEqual</tt>, when comparing two objects with the same 
+        number of undefined keys, but with different names.
+      </p>
+      
       <p>
         <b class="header">1.0.0</b><br />
         Things have been stable for many months now, so Underscore is now
diff --git a/package.json b/package.json
index e9fda74e8..197a47660 100644
--- a/package.json
+++ b/package.json
@@ -7,5 +7,5 @@
   "contributors"  : [],
   "dependencies"  : [],
   "lib"           : ".",
-  "version"       : "1.0.0"
+  "version"       : "1.0.1"
 }
diff --git a/test/objects.js b/test/objects.js
index a30b30e94..6b52fb2c3 100644
--- a/test/objects.js
+++ b/test/objects.js
@@ -58,6 +58,7 @@ $(document).ready(function() {
     ok(_.isEqual(new Date(100), new Date(100)), 'identical dates are equal');
     ok(_.isEqual((/hello/ig), (/hello/ig)), 'identical regexes are equal');
     ok(!_.isEqual(null, [1]), 'a falsy is never equal to a truthy');
+    ok(!_.isEqual({x: 1, y: undefined}, {x: 1, z: 2}), 'object with the same number of undefined keys are not equal');
   });
 
   test("objects: isEmpty", function() {
diff --git a/underscore-min.js b/underscore-min.js
index e3b1eb37d..189b2ab27 100644
--- a/underscore-min.js
+++ b/underscore-min.js
@@ -1,5 +1,5 @@
 (function(){var n=this,A=n._,r=typeof StopIteration!=="undefined"?StopIteration:"__break__",B=function(a){return a.replace(/([.*+?^${}()|[\]\/\\])/g,"\\$1")},j=Array.prototype,l=Object.prototype,o=j.slice,C=j.unshift,D=l.toString,p=l.hasOwnProperty,E=l.propertyIsEnumerable,s=j.forEach,t=j.map,u=j.reduce,v=j.reduceRight,w=j.filter,x=j.every,y=j.some,m=j.indexOf,z=j.lastIndexOf;l=Array.isArray;var F=Object.keys,b=function(a){return new k(a)};if(typeof exports!=="undefined")exports._=b;n._=b;b.VERSION=
-"1.0.0";var i=b.forEach=function(a,c,d){try{if(s&&a.forEach===s)a.forEach(c,d);else if(b.isNumber(a.length))for(var e=0,f=a.length;e<f;e++)c.call(d,a[e],e,a);else for(e in a)p.call(a,e)&&c.call(d,a[e],e,a)}catch(g){if(g!=r)throw g;}return a};b.map=function(a,c,d){if(t&&a.map===t)return a.map(c,d);var e=[];i(a,function(f,g,h){e.push(c.call(d,f,g,h))});return e};b.reduce=function(a,c,d,e){if(u&&a.reduce===u)return a.reduce(b.bind(d,e),c);i(a,function(f,g,h){c=d.call(e,c,f,g,h)});return c};b.reduceRight=
+"1.0.1";var i=b.forEach=function(a,c,d){try{if(s&&a.forEach===s)a.forEach(c,d);else if(b.isNumber(a.length))for(var e=0,f=a.length;e<f;e++)c.call(d,a[e],e,a);else for(e in a)p.call(a,e)&&c.call(d,a[e],e,a)}catch(g){if(g!=r)throw g;}return a};b.map=function(a,c,d){if(t&&a.map===t)return a.map(c,d);var e=[];i(a,function(f,g,h){e.push(c.call(d,f,g,h))});return e};b.reduce=function(a,c,d,e){if(u&&a.reduce===u)return a.reduce(b.bind(d,e),c);i(a,function(f,g,h){c=d.call(e,c,f,g,h)});return c};b.reduceRight=
 function(a,c,d,e){if(v&&a.reduceRight===v)return a.reduceRight(b.bind(d,e),c);a=b.clone(b.toArray(a)).reverse();return b.reduce(a,c,d,e)};b.detect=function(a,c,d){var e;i(a,function(f,g,h){if(c.call(d,f,g,h)){e=f;b.breakLoop()}});return e};b.filter=function(a,c,d){if(w&&a.filter===w)return a.filter(c,d);var e=[];i(a,function(f,g,h){c.call(d,f,g,h)&&e.push(f)});return e};b.reject=function(a,c,d){var e=[];i(a,function(f,g,h){!c.call(d,f,g,h)&&e.push(f)});return e};b.every=function(a,c,d){c=c||b.identity;
 if(x&&a.every===x)return a.every(c,d);var e=true;i(a,function(f,g,h){(e=e&&c.call(d,f,g,h))||b.breakLoop()});return e};b.some=function(a,c,d){c=c||b.identity;if(y&&a.some===y)return a.some(c,d);var e=false;i(a,function(f,g,h){if(e=c.call(d,f,g,h))b.breakLoop()});return e};b.include=function(a,c){if(m&&a.indexOf===m)return a.indexOf(c)!=-1;var d=false;i(a,function(e){if(d=e===c)b.breakLoop()});return d};b.invoke=function(a,c){var d=b.rest(arguments,2);return b.map(a,function(e){return(c?e[c]:e).apply(e,
 d)})};b.pluck=function(a,c){return b.map(a,function(d){return d[c]})};b.max=function(a,c,d){if(!c&&b.isArray(a))return Math.max.apply(Math,a);var e={computed:-Infinity};i(a,function(f,g,h){g=c?c.call(d,f,g,h):f;g>=e.computed&&(e={value:f,computed:g})});return e.value};b.min=function(a,c,d){if(!c&&b.isArray(a))return Math.min.apply(Math,a);var e={computed:Infinity};i(a,function(f,g,h){g=c?c.call(d,f,g,h):f;g<e.computed&&(e={value:f,computed:g})});return e.value};b.sortBy=function(a,c,d){return b.pluck(b.map(a,
@@ -9,7 +9,7 @@ e)))d.push(e);return d})};b.intersect=function(a){var c=b.rest(arguments);return
 for(var d=a.length;d--;)if(a[d]===c)return d;return-1};b.range=function(a,c,d){var e=b.toArray(arguments),f=e.length<=1;a=f?0:e[0];c=f?e[0]:e[1];d=e[2]||1;e=Math.ceil((c-a)/d);if(e<=0)return[];e=new Array(e);f=a;for(var g=0;;f+=d){if((d>0?f-c:c-f)>=0)return e;e[g++]=f}};b.bind=function(a,c){var d=b.rest(arguments,2);return function(){return a.apply(c||{},d.concat(b.toArray(arguments)))}};b.bindAll=function(a){var c=b.rest(arguments);if(c.length==0)c=b.functions(a);i(c,function(d){a[d]=b.bind(a[d],
 a)});return a};b.delay=function(a,c){var d=b.rest(arguments,2);return setTimeout(function(){return a.apply(a,d)},c)};b.defer=function(a){return b.delay.apply(b,[a,1].concat(b.rest(arguments)))};b.wrap=function(a,c){return function(){var d=[a].concat(b.toArray(arguments));return c.apply(c,d)}};b.compose=function(){var a=b.toArray(arguments);return function(){for(var c=b.toArray(arguments),d=a.length-1;d>=0;d--)c=[a[d].apply(this,c)];return c[0]}};b.keys=F||function(a){if(b.isArray(a))return b.range(0,
 a.length);var c=[];for(var d in a)p.call(a,d)&&c.push(d);return c};b.values=function(a){return b.map(a,b.identity)};b.functions=function(a){return b.filter(b.keys(a),function(c){return b.isFunction(a[c])}).sort()};b.extend=function(a){i(b.rest(arguments),function(c){for(var d in c)a[d]=c[d]});return a};b.clone=function(a){if(b.isArray(a))return a.slice(0);return b.extend({},a)};b.tap=function(a,c){c(a);return a};b.isEqual=function(a,c){if(a===c)return true;var d=typeof a;if(d!=typeof c)return false;
-if(a==c)return true;if(!a&&c||a&&!c)return false;if(a.isEqual)return a.isEqual(c);if(b.isDate(a)&&b.isDate(c))return a.getTime()===c.getTime();if(b.isNaN(a)&&b.isNaN(c))return true;if(b.isRegExp(a)&&b.isRegExp(c))return a.source===c.source&&a.global===c.global&&a.ignoreCase===c.ignoreCase&&a.multiline===c.multiline;if(d!=="object")return false;if(a.length&&a.length!==c.length)return false;d=b.keys(a);var e=b.keys(c);if(d.length!=e.length)return false;for(var f in a)if(!b.isEqual(a[f],c[f]))return false;
+if(a==c)return true;if(!a&&c||a&&!c)return false;if(a.isEqual)return a.isEqual(c);if(b.isDate(a)&&b.isDate(c))return a.getTime()===c.getTime();if(b.isNaN(a)&&b.isNaN(c))return true;if(b.isRegExp(a)&&b.isRegExp(c))return a.source===c.source&&a.global===c.global&&a.ignoreCase===c.ignoreCase&&a.multiline===c.multiline;if(d!=="object")return false;if(a.length&&a.length!==c.length)return false;d=b.keys(a);var e=b.keys(c);if(d.length!=e.length)return false;for(var f in a)if(!(f in c)||!b.isEqual(a[f],c[f]))return false;
 return true};b.isEmpty=function(a){if(b.isArray(a))return a.length===0;for(var c in a)if(p.call(a,c))return false;return true};b.isElement=function(a){return!!(a&&a.nodeType==1)};b.isArray=l||function(a){return!!(a&&a.concat&&a.unshift)};b.isArguments=function(a){return a&&b.isNumber(a.length)&&!a.concat&&!a.substr&&!a.apply&&!E.call(a,"length")};b.isFunction=function(a){return!!(a&&a.constructor&&a.call&&a.apply)};b.isString=function(a){return!!(a===""||a&&a.charCodeAt&&a.substr)};b.isNumber=function(a){return a===
 +a||D.call(a)==="[object Number]"};b.isBoolean=function(a){return a===true||a===false};b.isDate=function(a){return!!(a&&a.getTimezoneOffset&&a.setUTCFullYear)};b.isRegExp=function(a){return!!(a&&a.test&&a.exec&&(a.ignoreCase||a.ignoreCase===false))};b.isNaN=function(a){return b.isNumber(a)&&isNaN(a)};b.isNull=function(a){return a===null};b.isUndefined=function(a){return typeof a=="undefined"};b.noConflict=function(){n._=A;return this};b.identity=function(a){return a};b.times=function(a,c,d){for(var e=
 0;e<a;e++)c.call(d,e)};b.breakLoop=function(){throw r;};b.mixin=function(a){i(b.functions(a),function(c){G(c,b[c]=a[c])})};var H=0;b.uniqueId=function(a){var c=H++;return a?a+c:c};b.templateSettings={start:"<%",end:"%>",interpolate:/<%=(.+?)%>/g};b.template=function(a,c){var d=b.templateSettings,e=new RegExp("'(?=[^"+d.end.substr(0,1)+"]*"+B(d.end)+")","g");a=new Function("obj","var p=[],print=function(){p.push.apply(p,arguments);};with(obj){p.push('"+a.replace(/[\r\t\n]/g," ").replace(e,"\t").split("'").join("\\'").split("\t").join("'").replace(d.interpolate,
diff --git a/underscore.js b/underscore.js
index 52ce4f771..9a6c02f65 100644
--- a/underscore.js
+++ b/underscore.js
@@ -55,7 +55,7 @@
   root._ = _;
 
   // Current version.
-  _.VERSION = '1.0.0';
+  _.VERSION = '1.0.1';
 
   // ------------------------ Collection Functions: ---------------------------
 
@@ -485,7 +485,7 @@
     // Different object sizes?
     if (aKeys.length != bKeys.length) return false;
     // Recursive comparison of contents.
-    for (var key in a) if (!_.isEqual(a[key], b[key])) return false;
+    for (var key in a) if (!(key in b) || !_.isEqual(a[key], b[key])) return false;
     return true;
   };