diff --git a/core/focus_manager.ts b/core/focus_manager.ts
index 230bdf030..c6d40fa0d 100644
--- a/core/focus_manager.ts
+++ b/core/focus_manager.ts
@@ -148,7 +148,7 @@ export class FocusManager {
     if (!this.isRegistered(tree)) {
       throw Error(`Attempted to unregister not registered tree: ${tree}.`);
     }
-    const treeIndex = this.registeredTrees.findIndex((tree) => tree === tree);
+    const treeIndex = this.registeredTrees.findIndex((reg) => reg === tree);
     this.registeredTrees.splice(treeIndex, 1);
 
     const focusedNode = FocusableTreeTraverser.findFocusedNode(tree);
diff --git a/tests/mocha/focus_manager_test.js b/tests/mocha/focus_manager_test.js
index 70ef210c5..69ecfe722 100644
--- a/tests/mocha/focus_manager_test.js
+++ b/tests/mocha/focus_manager_test.js
@@ -305,6 +305,18 @@ suite('FocusManager', function () {
 
       assert.isTrue(isRegistered);
     });
+
+    test('for unregistered tree with other registered tree returns false', function () {
+      this.focusManager.registerTree(this.testFocusableTree2);
+      this.focusManager.registerTree(this.testFocusableTree1);
+      this.focusManager.unregisterTree(this.testFocusableTree1);
+
+      const isRegistered = this.focusManager.isRegistered(
+        this.testFocusableTree1,
+      );
+
+      assert.isFalse(isRegistered);
+    });
   });
 
   suite('getFocusedTree()', function () {