diff --git a/CHANGELOG b/CHANGELOG
index 2faa7e5..4e42982 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,7 @@
 *1.6.0_rc1* (October 16, 2007)
 
+* Fix Event#is(Left|Middle|Right)Click in IE.  Closes #7520 (again).  [Mislav Marohnić]
+
 * Ensure Event.* generic methods work in IE, even when the event is not extended. [Viktor Kojouharov, Andrew Dupont]
 
 * Don't translate "keypress" events into "keydown" events.  [sam]
diff --git a/src/event.js b/src/event.js
index 6c7ce63..b516b98 100644
--- a/src/event.js
+++ b/src/event.js
@@ -30,24 +30,27 @@ Object.extend(Event, {
 });
 
 Event.Methods = (function() {
+  var isButton;
+
   if (Prototype.Browser.IE) {
-    function isButton(event, code) {
-      return event.button == ({ 0: 1, 1: 4, 2: 2 })[code];
-    }
+    var buttonMap = { 0: 1, 1: 4, 2: 2 };
+    isButton = function(event, code) {
+      return event.button == buttonMap[code];
+    };
     
   } else if (Prototype.Browser.WebKit) {
-    function isButton(event, code) {
+    isButton = function(event, code) {
       switch (code) {
         case 0: return event.which == 1 && !event.metaKey;
         case 1: return event.which == 1 && event.metaKey;
         default: return false;
       }
-    }
+    };
     
   } else {
-    function isButton(event, code) {
+    isButton = function(event, code) {
       return event.which ? (event.which === code + 1) : (event.button === code);
-    }
+    };
   }
 
   return {