diff --git a/src/index.js b/src/index.js
index a80fcd3ac..ffdbe9671 100644
--- a/src/index.js
+++ b/src/index.js
@@ -344,8 +344,7 @@ class Dayjs {
   }
 
   daysInMonth() {
-    // clone is for badMutable plugin
-    return this.clone().endOf(C.M).$D
+    return this.endOf(C.M).$D
   }
 
   $locale() { // get locale object
diff --git a/src/plugin/badMutable/index.js b/src/plugin/badMutable/index.js
index 6d28124b4..f95d581c6 100644
--- a/src/plugin/badMutable/index.js
+++ b/src/plugin/badMutable/index.js
@@ -29,5 +29,25 @@ export default (o, c) => { // locale needed later
     this.$L = oldLocale.bind(this)(preset, object).$L
     return this
   }
+
+  const oldDaysInMonth = proto.daysInMonth
+  proto.daysInMonth = function () {
+    return oldDaysInMonth.bind(this.clone())()
+  }
+
+  const oldIsSame = proto.isSame
+  proto.isSame = function () {
+    return oldIsSame.bind(this.clone())()
+  }
+
+  const oldIsBefore = proto.isBefore
+  proto.isBefore = function () {
+    return oldIsBefore.bind(this.clone())()
+  }
+
+  const oldIsAfter = proto.isAfter
+  proto.isAfter = function () {
+    return oldIsAfter.bind(this.clone())()
+  }
 }
 
diff --git a/test/plugin/badMutable.test.js b/test/plugin/badMutable.test.js
index be9333251..e68128914 100644
--- a/test/plugin/badMutable.test.js
+++ b/test/plugin/badMutable.test.js
@@ -161,3 +161,14 @@ it('Locale', () => {
   expect(d.locale()).toBe(m.locale())
   expect(d.format(format)).toBe(m.format(format))
 })
+
+it('isAfter isBefore isSame', () => {
+  const d = dayjs()
+  const format = dayjs().format()
+  d.isSame(dayjs, 'year')
+  expect(d.format()).toBe(format)
+  d.isBefore(dayjs, 'hour')
+  expect(d.format()).toBe(format)
+  d.isAfter(dayjs, 'month')
+  expect(d.format()).toBe(format)
+})