diff --git a/src/plugin/customParseFormat/index.js b/src/plugin/customParseFormat/index.js
--- a/src/plugin/customParseFormat/index.js
+++ b/src/plugin/customParseFormat/index.js
@@ -175,6 +175,7 @@ function makeParser(format) {
 
 const parseFormattedInput = (input, format, utc) => {
   try {
+    if (['x', 'X'].indexOf(format) > -1) return new Date((format === 'X' ? 1000 : 1) * input)
     const parser = makeParser(format)
     const {
       year, month, day, hours, minutes, seconds, milliseconds, zone

diff --git a/test/plugin/customParseFormat.test.js b/test/plugin/customParseFormat.test.js
--- a/test/plugin/customParseFormat.test.js
+++ b/test/plugin/customParseFormat.test.js
@@ -368,3 +368,12 @@ it('custom two-digit year parse function', () => {
   const input3 = '99-05-02'
   expect(dayjs(input3, format).year()).toBe(1899)
 })
+
+it('parse X x', () => {
+  const input = '1410715640.579'
+  const format = 'X'
+  expect(dayjs(input, format).valueOf()).toBe(moment(input, format).valueOf())
+  const input2 = '1410715640579'
+  const format2 = 'x'
+  expect(dayjs(input2, format2).valueOf()).toBe(moment(input2, format2).valueOf())
+})

Parsing with Unix Timestamp tokens X/x and strict mode results in Invalid Date
**Describe the bug**

When `x` and `X` from [dayjs/plugin/advancedFormat](https://day.js.org/docs/en/plugin/advanced-format) is used with strict mode parse fails:
```js
dayjs(`/Date(${dayjs().format('x')})/`,"/[Date](x)/").format('/[Date](x)/')
> "/Date(1623787200000)/"
dayjs(`/Date(${dayjs().format('X')})/`,"/[Date](X)/").format('/[Date](X)/')
> "/Date(1623787200)/"

dayjs(`/Date(${dayjs().format('x')})/`,"/[Date](x)/",true).format('/[Date](x)/')
> "Invalid Date"
dayjs(`/Date(${dayjs().format('X')})/`,"/[Date](X)/",true).format('/[Date](X)/')
> "Invalid Date"
```
**Expected behavior**
last 2 examples should parse correctly as fist 2 cases do.

**Information**
tested on recent version of chrome (in dev tools of https://day.js.org/)

looks like related to:
https://github.com/iamkun/dayjs/pull/1467
https://github.com/iamkun/dayjs/issues/929
https://github.com/iamkun/dayjs/pull/1467

test/timezone.test.js(1) test/timezone.test.js(2) test/timezone.test.js(3) test/timezone.test.js(4)
test/plugin/customParseFormat.test.js