diff --git a/test/functions.js b/test/functions.js
index 96292b563..b976977e7 100644
--- a/test/functions.js
+++ b/test/functions.js
@@ -76,7 +76,7 @@ $(document).ready(function() {
     setTimeout(throttledIncr, 70);
     setTimeout(throttledIncr, 110);
     setTimeout(throttledIncr, 120);
-    _.delay(function(){ ok(counter == 3, "incr was throttled"); start(); }, 180);
+    _.delay(function(){ ok(counter == 3, "incr was throttled"); start(); }, 200);
   });
 
   asyncTest("functions: debounce", 1, function() {
diff --git a/test/objects.js b/test/objects.js
index 04577994a..b47de7fc4 100644
--- a/test/objects.js
+++ b/test/objects.js
@@ -86,7 +86,7 @@ $(document).ready(function() {
       parent.iRegExp    = /hi/;\
       parent.iNaN       = NaN;\
       parent.iNull      = null;\
-	  parent.iBoolean   = false;\
+      parent.iBoolean   = false;\
       parent.iUndefined = undefined;\
     </script>"
   );
@@ -125,7 +125,7 @@ $(document).ready(function() {
     ok(!_.isNumber(arguments), 'the arguments object is not a number');
     ok(!_.isNumber(undefined), 'undefined is not a number');
     ok(_.isNumber(3 * 4 - 7 / 10), 'but numbers are');
-    ok(_.isNumber(NaN), 'NaN is a number');
+    ok(!_.isNumber(NaN), 'NaN is not a number');
     ok(_.isNumber(Infinity), 'Infinity is a number');
     ok(_.isNumber(iNumber), 'even from another frame');
   });
@@ -183,11 +183,24 @@ $(document).ready(function() {
     ok(!_.isUndefined(1), 'numbers are defined');
     ok(!_.isUndefined(null), 'null is defined');
     ok(!_.isUndefined(false), 'false is defined');
+    ok(!_.isUndefined(NaN), 'NaN is defined');
     ok(_.isUndefined(), 'nothing is undefined');
     ok(_.isUndefined(undefined), 'undefined is undefined');
     ok(_.isUndefined(iUndefined), 'even from another frame');
   });
 
+  if (window.ActiveXObject) {
+    test("objects: IE host objects", function() {
+      var xml = new ActiveXObject("Msxml2.DOMDocument.3.0");
+      ok(!_.isNumber(xml));
+      ok(!_.isBoolean(xml));
+      ok(!_.isNaN(xml));
+      ok(!_.isFunction(xml));
+      ok(!_.isNull(xml));
+      ok(!_.isUndefined(xml));
+    });
+  }
+
   test("objects: tap", function() {
     var intercepted = null;
     var interceptor = function(obj) { intercepted = obj; };
diff --git a/underscore.js b/underscore.js
index 33925ded8..291b97617 100644
--- a/underscore.js
+++ b/underscore.js
@@ -588,7 +588,13 @@
 
   // Is a given value a number?
   _.isNumber = function(obj) {
-    return (obj === +obj) || (toString.call(obj) === '[object Number]');
+    return !!(obj === 0 || (obj && obj.toExponential && obj.toFixed));
+  };
+
+  // Is the given value NaN -- this one is interesting. NaN != NaN, and
+  // isNaN(undefined) == true, so we make sure it's a number first.
+  _.isNaN = function(obj) {
+    return toString.call(obj) === '[object Number]' && isNaN(obj);
   };
 
   // Is a given value a boolean?
@@ -606,12 +612,6 @@
     return !!(obj && obj.test && obj.exec && (obj.ignoreCase || obj.ignoreCase === false));
   };
 
-  // Is the given value NaN -- this one is interesting. NaN != NaN, and
-  // isNaN(undefined) == true, so we make sure it's a number first.
-  _.isNaN = function(obj) {
-    return _.isNumber(obj) && isNaN(obj);
-  };
-
   // Is a given value equal to null?
   _.isNull = function(obj) {
     return obj === null;
@@ -619,7 +619,7 @@
 
   // Is a given variable undefined?
   _.isUndefined = function(obj) {
-    return typeof obj == 'undefined';
+    return obj === void 0;
   };
 
   // Utility Functions