diff --git a/src/io/mouse.js b/src/io/mouse.js
index 47c6a498..508248d0 100644
--- a/src/io/mouse.js
+++ b/src/io/mouse.js
@@ -5,6 +5,7 @@ class Mouse {
         this._x = 0;
         this._y = 0;
         this._buttons = new Set();
+        this.usesRightClickDown = false;
         this._isDown = false;
         /**
          * Reference to the owning Runtime.
@@ -156,6 +157,9 @@ class Mouse {
      * @return {boolean} Is the mouse button down?
      */
     getButtonIsDown (button) {
+        if (button === 2) {
+            this.usesRightClickDown = true;
+        }
         return this._buttons.has(button);
     }
 }
diff --git a/test/unit/io_mouse.js b/test/unit/io_mouse.js
index d9966123..d672bc08 100644
--- a/test/unit/io_mouse.js
+++ b/test/unit/io_mouse.js
@@ -108,7 +108,7 @@ test('mouseDown with buttons', t => {
     t.end();
 });
 
-test('no button is treated as left', t => {
+test('missing button is treated as left', t => {
     const rt = new Runtime();
     const m = new Mouse(rt);
 
@@ -124,6 +124,16 @@ test('no button is treated as left', t => {
     t.end();
 });
 
+test('usesRightClickDown', t => {
+    const rt = new Runtime();
+    const m = new Mouse(rt);
+
+    t.strictEquals(m.usesRightClickDown, false);
+    t.strictEquals(m.getButtonIsDown(2), false);
+    t.strictEquals(m.usesRightClickDown, true);
+    t.end();
+});
+
 test('at zoomed scale', t => {
     const rt = new Runtime();
     const m = new Mouse(rt);