diff --git a/cjs/dom/token-list.js b/cjs/dom/token-list.js
index 25f70f1d..cc4cfe67 100644
--- a/cjs/dom/token-list.js
+++ b/cjs/dom/token-list.js
@@ -73,7 +73,7 @@ class DOMTokenList extends Set {
       this.delete(token);
       update(this);
     }
-    else if (force || arguments.length === 1) {
+    else if (force || force === undefined) {
       super.add(token);
       update(this);
       return true;
diff --git a/esm/dom/token-list.js b/esm/dom/token-list.js
index 27c19ff7..8efc4a32 100644
--- a/esm/dom/token-list.js
+++ b/esm/dom/token-list.js
@@ -72,7 +72,7 @@ export class DOMTokenList extends Set {
       this.delete(token);
       update(this);
     }
-    else if (force || arguments.length === 1) {
+    else if (force || force === undefined) {
       super.add(token);
       update(this);
       return true;
diff --git a/test/html/element.js b/test/html/element.js
index 3c3fedd8..59ae94ac 100644
--- a/test/html/element.js
+++ b/test/html/element.js
@@ -75,6 +75,11 @@ node.classList.toggle('test', true);
 assert(node.classList.contains('test'), true, 'test class still in');
 node.classList.toggle('test', false);
 node.classList.toggle('test', true);
+// issue #277: explicit undefined force must behave like an omitted argument
+assert(node.classList.toggle('test', undefined), false, 'toggle(test, undefined) when present removes and returns false');
+assert(node.classList.contains('test'), false, 'no test class after toggle(test, undefined)');
+assert(node.classList.toggle('test', undefined), true, 'toggle(test, undefined) when absent adds and returns true');
+assert(node.classList.contains('test'), true, 'test class added by toggle(test, undefined)');
 node.classList.remove('test');
 assert(node.classList.contains('test'), false, 'no test class one more time');
 assert(node.classList.replace('b', 'c'), true, 'replace happened');