diff --git a/src/plugin/customParseFormat/index.js b/src/plugin/customParseFormat/index.js
index 73e48eb91..fc3b788f4 100644
--- a/src/plugin/customParseFormat/index.js
+++ b/src/plugin/customParseFormat/index.js
@@ -232,7 +232,10 @@ export default (o, C, d) => {
       this.$d = parseFormattedInput(date, format, utc)
       this.init()
       if (pl && pl !== true) this.$L = this.locale(pl).$L
-      if (isStrict && date !== this.format(format)) {
+      // use != to treat
+      // input number 1410715640579 and format string '1410715640579' equal
+      // eslint-disable-next-line eqeqeq
+      if (isStrict && date != this.format(format)) {
         this.$d = new Date('')
       }
       // reset global locale to make parallel unit test
diff --git a/test/plugin/customParseFormat.test.js b/test/plugin/customParseFormat.test.js
index 97fe8fb73..3b4e5f9cb 100644
--- a/test/plugin/customParseFormat.test.js
+++ b/test/plugin/customParseFormat.test.js
@@ -5,6 +5,7 @@ import '../../src/locale/ru'
 import uk from '../../src/locale/uk'
 import '../../src/locale/zh-cn'
 import customParseFormat from '../../src/plugin/customParseFormat'
+import advancedFormat from '../../src/plugin/advancedFormat'
 import localizedFormats from '../../src/plugin/localizedFormat'
 
 dayjs.extend(customParseFormat)
@@ -376,4 +377,8 @@ it('parse X x', () => {
   const input2 = '1410715640579'
   const format2 = 'x'
   expect(dayjs(input2, format2).valueOf()).toBe(moment(input2, format2).valueOf())
+
+  // x X starct parse requires advancedFormat plugin
+  dayjs.extend(advancedFormat)
+  expect(dayjs(input2, format2, true).valueOf()).toBe(moment(input2, format2, true).valueOf())
 })