diff --git a/src/plugin/badMutable/index.js b/src/plugin/badMutable/index.js
index f95d581c6..c82aafb67 100644
--- a/src/plugin/badMutable/index.js
+++ b/src/plugin/badMutable/index.js
@@ -36,18 +36,18 @@ export default (o, c) => { // locale needed later
   }
 
   const oldIsSame = proto.isSame
-  proto.isSame = function () {
-    return oldIsSame.bind(this.clone())()
+  proto.isSame = function (that, units) {
+    return oldIsSame.bind(this.clone())(that, units)
   }
 
   const oldIsBefore = proto.isBefore
-  proto.isBefore = function () {
-    return oldIsBefore.bind(this.clone())()
+  proto.isBefore = function (that, units) {
+    return oldIsBefore.bind(this.clone())(that, units)
   }
 
   const oldIsAfter = proto.isAfter
-  proto.isAfter = function () {
-    return oldIsAfter.bind(this.clone())()
+  proto.isAfter = function (that, units) {
+    return oldIsAfter.bind(this.clone())(that, units)
   }
 }
 
diff --git a/test/plugin/badMutable.test.js b/test/plugin/badMutable.test.js
index e68128914..5b38bc899 100644
--- a/test/plugin/badMutable.test.js
+++ b/test/plugin/badMutable.test.js
@@ -167,8 +167,11 @@ it('isAfter isBefore isSame', () => {
   const format = dayjs().format()
   d.isSame(dayjs, 'year')
   expect(d.format()).toBe(format)
+  expect(d.isSame()).toBe(true)
   d.isBefore(dayjs, 'hour')
   expect(d.format()).toBe(format)
+  expect(d.isBefore()).toBe(false)
   d.isAfter(dayjs, 'month')
   expect(d.format()).toBe(format)
+  expect(d.isAfter()).toBe(false)
 })