diff --git a/src/lib/es2020.intl.d.ts b/src/lib/es2020.intl.d.ts
index ba57d2e8658..581e9fb15cd 100644
--- a/src/lib/es2020.intl.d.ts
+++ b/src/lib/es2020.intl.d.ts
@@ -288,7 +288,7 @@ declare namespace Intl {
      * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Locale).
      */
     const Locale: {
-        new (tag?: BCP47LanguageTag, options?: LocaleOptions): Locale;
+        new (tag: BCP47LanguageTag | Locale, options?: LocaleOptions): Locale;
     };
 
      interface DisplayNamesOptions {
diff --git a/tests/baselines/reference/es2020IntlAPIs.errors.txt b/tests/baselines/reference/es2020IntlAPIs.errors.txt
new file mode 100644
index 00000000000..0c74f13974c
--- /dev/null
+++ b/tests/baselines/reference/es2020IntlAPIs.errors.txt
@@ -0,0 +1,53 @@
+tests/cases/conformance/es2020/es2020IntlAPIs.ts(45,1): error TS2554: Expected 1-2 arguments, but got 0.
+
+
+==== tests/cases/conformance/es2020/es2020IntlAPIs.ts (1 errors) ====
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_identification_and_negotiation
+    const count = 26254.39;
+    const date = new Date("2012-05-24");
+    
+    function log(locale: string) {
+      console.log(
+        `${new Intl.DateTimeFormat(locale).format(date)} ${new Intl.NumberFormat(locale).format(count)}`
+      );
+    }
+    
+    log("en-US");
+    // expected output: 5/24/2012 26,254.39
+    
+    log("de-DE");
+    // expected output: 24.5.2012 26.254,39
+    
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat
+    const rtf1 = new Intl.RelativeTimeFormat('en', { style: 'narrow' });
+    
+    console.log(rtf1.format(3, 'quarter'));
+    //expected output: "in 3 qtrs."
+    
+    console.log(rtf1.format(-1, 'day'));
+    //expected output: "1 day ago"
+    
+    const rtf2 = new Intl.RelativeTimeFormat('es', { numeric: 'auto' });
+    
+    console.log(rtf2.format(2, 'day'));
+    //expected output: "pasado mañana"
+    
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DisplayNames
+    const regionNamesInEnglish = new Intl.DisplayNames(['en'], { type: 'region' });
+    const regionNamesInTraditionalChinese = new Intl.DisplayNames(['zh-Hant'], { type: 'region' });
+    
+    console.log(regionNamesInEnglish.of('US'));
+    // expected output: "United States"
+    
+    console.log(regionNamesInTraditionalChinese.of('US'));
+    // expected output: "美國"
+    
+    const locales1 = ['ban', 'id-u-co-pinyin', 'de-ID'];
+    const options1 = { localeMatcher: 'lookup' } as const;
+    console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '));
+    
+    new Intl.Locale(); // should error
+    ~~~~~~~~~~~~~~~~~
+!!! error TS2554: Expected 1-2 arguments, but got 0.
+!!! related TS6210 /.ts/lib.es2020.intl.d.ts:311:14: An argument for 'tag' was not provided.
+    new Intl.Locale(new Intl.Locale('en-US'));
\ No newline at end of file
diff --git a/tests/baselines/reference/es2020IntlAPIs.js b/tests/baselines/reference/es2020IntlAPIs.js
index 8136ff27ee0..d08c2f427cd 100644
--- a/tests/baselines/reference/es2020IntlAPIs.js
+++ b/tests/baselines/reference/es2020IntlAPIs.js
@@ -41,7 +41,10 @@ console.log(regionNamesInTraditionalChinese.of('US'));
 
 const locales1 = ['ban', 'id-u-co-pinyin', 'de-ID'];
 const options1 = { localeMatcher: 'lookup' } as const;
-console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '));
+console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '));
+
+new Intl.Locale(); // should error
+new Intl.Locale(new Intl.Locale('en-US'));
 
 //// [es2020IntlAPIs.js]
 // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#Locale_identification_and_negotiation
@@ -73,3 +76,5 @@ console.log(regionNamesInTraditionalChinese.of('US'));
 const locales1 = ['ban', 'id-u-co-pinyin', 'de-ID'];
 const options1 = { localeMatcher: 'lookup' };
 console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '));
+new Intl.Locale(); // should error
+new Intl.Locale(new Intl.Locale('en-US'));
diff --git a/tests/baselines/reference/es2020IntlAPIs.symbols b/tests/baselines/reference/es2020IntlAPIs.symbols
index 1738ba245b9..08986c4bf7d 100644
--- a/tests/baselines/reference/es2020IntlAPIs.symbols
+++ b/tests/baselines/reference/es2020IntlAPIs.symbols
@@ -147,3 +147,16 @@ console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '))
 >options1 : Symbol(options1, Decl(es2020IntlAPIs.ts, 41, 5))
 >join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
 
+new Intl.Locale(); // should error
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
+new Intl.Locale(new Intl.Locale('en-US'));
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
diff --git a/tests/baselines/reference/es2020IntlAPIs.types b/tests/baselines/reference/es2020IntlAPIs.types
index 4a5332ed64c..fa7ab907a19 100644
--- a/tests/baselines/reference/es2020IntlAPIs.types
+++ b/tests/baselines/reference/es2020IntlAPIs.types
@@ -207,3 +207,20 @@ console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '))
 >join : (separator?: string) => string
 >', ' : ", "
 
+new Intl.Locale(); // should error
+>new Intl.Locale() : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+
+new Intl.Locale(new Intl.Locale('en-US'));
+>new Intl.Locale(new Intl.Locale('en-US')) : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>new Intl.Locale('en-US') : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>'en-US' : "en-US"
+
diff --git a/tests/baselines/reference/localesObjectArgument.types b/tests/baselines/reference/localesObjectArgument.types
index a7a07a6ce6a..efaca6926db 100644
--- a/tests/baselines/reference/localesObjectArgument.types
+++ b/tests/baselines/reference/localesObjectArgument.types
@@ -2,25 +2,25 @@
 const enUS = new Intl.Locale("en-US");
 >enUS : Intl.Locale
 >new Intl.Locale("en-US") : Intl.Locale
->Intl.Locale : new (tag?: string, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
 >Intl : typeof Intl
->Locale : new (tag?: string, options?: Intl.LocaleOptions) => Intl.Locale
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
 >"en-US" : "en-US"
 
 const deDE = new Intl.Locale("de-DE");
 >deDE : Intl.Locale
 >new Intl.Locale("de-DE") : Intl.Locale
->Intl.Locale : new (tag?: string, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
 >Intl : typeof Intl
->Locale : new (tag?: string, options?: Intl.LocaleOptions) => Intl.Locale
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
 >"de-DE" : "de-DE"
 
 const jaJP = new Intl.Locale("ja-JP");
 >jaJP : Intl.Locale
 >new Intl.Locale("ja-JP") : Intl.Locale
->Intl.Locale : new (tag?: string, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
 >Intl : typeof Intl
->Locale : new (tag?: string, options?: Intl.LocaleOptions) => Intl.Locale
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
 >"ja-JP" : "ja-JP"
 
 const now = new Date();
diff --git a/tests/cases/conformance/es2020/es2020IntlAPIs.ts b/tests/cases/conformance/es2020/es2020IntlAPIs.ts
index 464ecc01ecf..70c52a0de3d 100644
--- a/tests/cases/conformance/es2020/es2020IntlAPIs.ts
+++ b/tests/cases/conformance/es2020/es2020IntlAPIs.ts
@@ -42,4 +42,7 @@ console.log(regionNamesInTraditionalChinese.of('US'));
 
 const locales1 = ['ban', 'id-u-co-pinyin', 'de-ID'];
 const options1 = { localeMatcher: 'lookup' } as const;
-console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '));
\ No newline at end of file
+console.log(Intl.DisplayNames.supportedLocalesOf(locales1, options1).join(', '));
+
+new Intl.Locale(); // should error
+new Intl.Locale(new Intl.Locale('en-US'));
\ No newline at end of file