diff --git a/core/input/mouse.js b/core/input/mouse.js
index 4d015669..8c917d09 100644
--- a/core/input/mouse.js
+++ b/core/input/mouse.js
@@ -42,16 +42,7 @@ export default class Mouse {
         this._updateMousePosition(e);
         let pos = this._pos;
 
-        let bmask;
-        if (e.which) {
-            /* everything except IE */
-            bmask = 1 << e.button;
-        } else {
-            /* IE including 9 */
-            bmask = (e.button & 0x1) +      // Left
-                    (e.button & 0x2) * 2 +  // Right
-                    (e.button & 0x4) / 2;   // Middle
-        }
+        let bmask = 1 << e.button;
 
         Log.Debug("onmousebutton " + (down ? "down" : "up") +
                   ", x: " + pos.x + ", y: " + pos.y + ", bmask: " + bmask);
diff --git a/tests/test.mouse.js b/tests/test.mouse.js
index 9e06ff26..13bd0c60 100644
--- a/tests/test.mouse.js
+++ b/tests/test.mouse.js
@@ -43,7 +43,7 @@ describe('Mouse Event Handling', function () {
                 expect(down).to.be.equal(1);
                 done();
             };
-            mouse._handleMouseDown(mouseevent('mousedown', { button: '0x01' }));
+            mouse._handleMouseDown(mouseevent('mousedown', { button: 0 }));
         });
         it('should decode mouseup events', function (done) {
             let calls = 0;
@@ -55,8 +55,8 @@ describe('Mouse Event Handling', function () {
                     done();
                 }
             };
-            mouse._handleMouseDown(mouseevent('mousedown', { button: '0x01' }));
-            mouse._handleMouseUp(mouseevent('mouseup', { button: '0x01' }));
+            mouse._handleMouseDown(mouseevent('mousedown', { button: 0 }));
+            mouse._handleMouseUp(mouseevent('mouseup', { button: 0 }));
         });
         it('should decode mousemove events', function (done) {
             const mouse = new Mouse(target);