diff --git a/models/session.js b/models/session.js
index 3a07a88..f101a5a 100644
--- a/models/session.js
+++ b/models/session.js
@@ -130,7 +130,7 @@ export default class Session extends EventTarget {
   /** Add another round if there is no current one. */
   anotherGame() {
     if (this.#currentGame === null) {
-      this.#currentGame = new Game(this.rules);
+      this.#currentGame = new Game(new GameRules(this.#rules));
       this.#currentGame.addEventListener(
         Game.EVENT_CHANGE, this.#boundHandleGameChange);
       this.#changed();
diff --git a/models/session.test.js b/models/session.test.js
index b727450..b444e6f 100644
--- a/models/session.test.js
+++ b/models/session.test.js
@@ -60,6 +60,17 @@ export default function() {
       assert.notStrictEqual(session.currentGame, null, "game in progress");
     });
 
+    QUnit.test("session rule change doesn't affect games", function(assert) {
+      let session = new Session();
+      session.anotherGame();
+      session.rules.goal = 7;
+      assert.notStrictEqual(
+        session.currentGame.rules.goal,
+        session.rules.goal,
+        "game rules have been copied",
+      );
+    });
+
     QUnit.test("single game finished", function(assert) {
       let session = new Session();
       session.anotherGame();