diff --git a/lib/ace/lib/event.js b/lib/ace/lib/event.js
index b9f3ebe4..06932d3c 100644
--- a/lib/ace/lib/event.js
+++ b/lib/ace/lib/event.js
@@ -241,12 +241,11 @@ function normalizeCommandKeys(callback, e, keyCode) {
         if (keyCode === 18 || keyCode === 17) {
             var location = "location" in e ? e.location : e.keyLocation;
             if (keyCode === 17 && location === 1) {
-                ts = e.timeStamp;
+                if (pressedKeys[keyCode] == 1)
+                    ts = e.timeStamp;
             } else if (keyCode === 18 && hashId === 3 && location === 2) {
-                var dt = -ts;
-                ts = e.timeStamp;
-                dt += ts;
-                if (dt < 3)
+                var dt = e.timestamp - ts;
+                if (dt < 50)
                     pressedKeys.altGr = true;
             }
         }
@@ -309,7 +308,7 @@ exports.addCommandKeyListener = function(el, callback) {
         var lastDefaultPrevented = null;
 
         addListener(el, "keydown", function(e) {
-            pressedKeys[e.keyCode] = true;
+            pressedKeys[e.keyCode] = (pressedKeys[e.keyCode] || 0) + 1;
             var result = normalizeCommandKeys(callback, e, e.keyCode);
             lastDefaultPrevented = e.defaultPrevented;
             return result;