diff --git a/tsc/internal/bundled/libs/lib.esnext.temporal.d.ts b/tsc/internal/bundled/libs/lib.esnext.temporal.d.ts
index 2d18011132a25..b27f5bf30c5c7 100644
--- a/tsc/internal/bundled/libs/lib.esnext.temporal.d.ts
+++ b/tsc/internal/bundled/libs/lib.esnext.temporal.d.ts
@@ -272,6 +272,10 @@ declare namespace Temporal {
         timeZoneName?: "auto" | "never" | "critical" | undefined;
     }
 
+    interface ZonedDateTimeToLocaleStringOptions extends Intl.DateTimeFormatOptions {
+        timeZone?: never;
+    }
+
     interface ZonedDateTimeFromOptions extends OverflowOptions, DisambiguationOptions {
         offset?: "use" | "ignore" | "prefer" | "reject" | undefined;
     }
@@ -317,7 +321,7 @@ declare namespace Temporal {
         round(roundTo: RoundingOptions<"day" | TimeUnit>): ZonedDateTime;
         equals(other: ZonedDateTimeLike): boolean;
         toString(options?: ZonedDateTimeToStringOptions): string;
-        toLocaleString(locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions): string;
+        toLocaleString(locales?: Intl.LocalesArgument, options?: ZonedDateTimeToLocaleStringOptions): string;
         toJSON(): string;
         valueOf(): never;
         startOfDay(): ZonedDateTime;
diff --git a/tsc/testdata/baselines/reference/compiler/temporal.errors.txt b/tsc/testdata/baselines/reference/compiler/temporal.errors.txt
index 59d4e125441bd..df73f0ee79e07 100644
--- a/tsc/testdata/baselines/reference/compiler/temporal.errors.txt
+++ b/tsc/testdata/baselines/reference/compiler/temporal.errors.txt
@@ -1,10 +1,15 @@
 temporal.ts(25,13): error TS2339: Property 'year' does not exist on type 'Instant'.
+temporal.ts(594,47): error TS2322: Type 'string' is not assignable to type 'undefined'.
 temporal.ts(1504,8): error TS2339: Property 'month' does not exist on type 'PlainMonthDay'.
 temporal.ts(1514,8): error TS2339: Property 'month' does not exist on type 'PlainMonthDay'.
 temporal.ts(1520,8): error TS2339: Property 'month' does not exist on type 'PlainMonthDay'.
+temporal.ts(1826,45): error TS2345: Argument of type 'DateTimeFormatOptions' is not assignable to parameter of type 'ZonedDateTimeToLocaleStringOptions'.
+  Types of property 'timeZone' are incompatible.
+    Type 'string | undefined' is not assignable to type 'undefined'.
+      Type 'string' is not assignable to type 'undefined'.
 
 
-==== temporal.ts (4 errors) ====
+==== temporal.ts (6 errors) ====
     /**
      * Test cases derived from documentation at tc39/proposal-temporal,
      * under the following license:
@@ -601,6 +606,8 @@ temporal.ts(1520,8): error TS2339: Property 'month' does not exist on type 'Plai
         const options = { weekday: "long", year: "numeric", month: "long", day: "numeric" } as const;
         zdt.toLocaleString("de-DE", options); // => 'Sonntag, 1. Dezember 2019'
         /* WRONG */ zdt.toLocaleString("de-DE", { timeZone: "Pacific/Auckland" });
+                                                  ~~~~~~~~
+!!! error TS2322: Type 'string' is not assignable to type 'undefined'.
         // => RangeError: Time zone option Pacific/Auckland does not match actual time zone Europe/Berlin
         zdt.withTimeZone("Pacific/Auckland").toLocaleString("de-DE"); // => '2.12.2019, 0:00:00 GMT+13'
         zdt.toLocaleString("en-US-u-nu-fullwide-hc-h12"); // => '１２/１/２０１９, １２:００:００ PM GMT+１'
@@ -1833,4 +1840,16 @@ temporal.ts(1520,8): error TS2339: Property 'month' does not exist on type 'Plai
         Temporal.Now.plainTimeISO(); // get the current wall-clock time in the system time zone and ISO-8601 calendar
         Temporal.Now.plainDateTimeISO(); // same as above, but return the DateTime in the ISO-8601 calendar
     }
+    
+    {
+        // Refused through a widened variable too, not only in an object literal.
+        const zdt = Temporal.ZonedDateTime.from("2019-12-01T12:00+01:00[Europe/Berlin]");
+        const widened: Intl.DateTimeFormatOptions = { timeZone: "Pacific/Auckland" };
+        /* WRONG */ zdt.toLocaleString("de-DE", widened);
+                                                ~~~~~~~
+!!! error TS2345: Argument of type 'DateTimeFormatOptions' is not assignable to parameter of type 'ZonedDateTimeToLocaleStringOptions'.
+!!! error TS2345:   Types of property 'timeZone' are incompatible.
+!!! error TS2345:     Type 'string | undefined' is not assignable to type 'undefined'.
+!!! error TS2345:       Type 'string' is not assignable to type 'undefined'.
+    }
     
\ No newline at end of file
diff --git a/tsc/testdata/baselines/reference/compiler/temporal.js b/tsc/testdata/baselines/reference/compiler/temporal.js
index 951ddf52662ec..7086a2fbfa169 100644
--- a/tsc/testdata/baselines/reference/compiler/temporal.js
+++ b/tsc/testdata/baselines/reference/compiler/temporal.js
@@ -1821,6 +1821,13 @@
     Temporal.Now.plainTimeISO(); // get the current wall-clock time in the system time zone and ISO-8601 calendar
     Temporal.Now.plainDateTimeISO(); // same as above, but return the DateTime in the ISO-8601 calendar
 }
+
+{
+    // Refused through a widened variable too, not only in an object literal.
+    const zdt = Temporal.ZonedDateTime.from("2019-12-01T12:00+01:00[Europe/Berlin]");
+    const widened: Intl.DateTimeFormatOptions = { timeZone: "Pacific/Auckland" };
+    /* WRONG */ zdt.toLocaleString("de-DE", widened);
+}
 
 
 //// [temporal.js]
@@ -3371,3 +3378,9 @@
     Temporal.Now.plainTimeISO(); // get the current wall-clock time in the system time zone and ISO-8601 calendar
     Temporal.Now.plainDateTimeISO(); // same as above, but return the DateTime in the ISO-8601 calendar
 }
+{
+    // Refused through a widened variable too, not only in an object literal.
+    const zdt = Temporal.ZonedDateTime.from("2019-12-01T12:00+01:00[Europe/Berlin]");
+    const widened = { timeZone: "Pacific/Auckland" };
+    /* WRONG */ zdt.toLocaleString("de-DE", widened);
+}
diff --git a/tsc/testdata/baselines/reference/compiler/temporal.symbols b/tsc/testdata/baselines/reference/compiler/temporal.symbols
index f232e7509e447..afed1f0d5b854 100644
--- a/tsc/testdata/baselines/reference/compiler/temporal.symbols
+++ b/tsc/testdata/baselines/reference/compiler/temporal.symbols
@@ -7029,3 +7029,26 @@
 >plainDateTimeISO : Symbol(Temporal.Now.plainDateTimeISO, Decl(lib.esnext.temporal.d.ts, --, --))
 }
 
+{
+    // Refused through a widened variable too, not only in an object literal.
+    const zdt = Temporal.ZonedDateTime.from("2019-12-01T12:00+01:00[Europe/Berlin]");
+>zdt : Symbol(zdt, Decl(temporal.ts, 1823, 9))
+>Temporal.ZonedDateTime.from : Symbol(Temporal.ZonedDateTimeConstructor.from, Decl(lib.esnext.temporal.d.ts, --, --))
+>Temporal.ZonedDateTime : Symbol(Temporal.ZonedDateTime, Decl(lib.esnext.temporal.d.ts, --, --), Decl(lib.esnext.temporal.d.ts, --, --))
+>Temporal : Symbol(Temporal, Decl(lib.esnext.temporal.d.ts, --, --))
+>ZonedDateTime : Symbol(Temporal.ZonedDateTime, Decl(lib.esnext.temporal.d.ts, --, --), Decl(lib.esnext.temporal.d.ts, --, --))
+>from : Symbol(Temporal.ZonedDateTimeConstructor.from, Decl(lib.esnext.temporal.d.ts, --, --))
+
+    const widened: Intl.DateTimeFormatOptions = { timeZone: "Pacific/Auckland" };
+>widened : Symbol(widened, Decl(temporal.ts, 1824, 9))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2025.intl.d.ts, --, --) ... and 1 more)
+>DateTimeFormatOptions : Symbol(Intl.DateTimeFormatOptions, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>timeZone : Symbol(timeZone, Decl(temporal.ts, 1824, 49))
+
+    /* WRONG */ zdt.toLocaleString("de-DE", widened);
+>zdt.toLocaleString : Symbol(Temporal.ZonedDateTime.toLocaleString, Decl(lib.esnext.temporal.d.ts, --, --))
+>zdt : Symbol(zdt, Decl(temporal.ts, 1823, 9))
+>toLocaleString : Symbol(Temporal.ZonedDateTime.toLocaleString, Decl(lib.esnext.temporal.d.ts, --, --))
+>widened : Symbol(widened, Decl(temporal.ts, 1824, 9))
+}
+
diff --git a/tsc/testdata/baselines/reference/compiler/temporal.types b/tsc/testdata/baselines/reference/compiler/temporal.types
index 39088d06c4f34..6533709ebba9e 100644
--- a/tsc/testdata/baselines/reference/compiler/temporal.types
+++ b/tsc/testdata/baselines/reference/compiler/temporal.types
@@ -1598,9 +1598,9 @@
 >zdt => zdt.toLocaleString("en", { month: "long" }) : (zdt: Temporal.ZonedDateTime) => string
 >zdt : Temporal.ZonedDateTime
 >zdt.toLocaleString("en", { month: "long" }) : string
->zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >zdt : Temporal.ZonedDateTime
->toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >"en" : "en"
 >{ month: "long" } : { month: "long"; }
 >month : "long"
@@ -2604,15 +2604,15 @@
 
     zdt.toLocaleString(); // example output: 12/1/2019, 12:00:00 PM
 >zdt.toLocaleString() : string
->zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >zdt : Temporal.ZonedDateTime
->toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 
     zdt.toLocaleString("de-DE"); // => '1.12.2019, 12:00:00 MEZ'
 >zdt.toLocaleString("de-DE") : string
->zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >zdt : Temporal.ZonedDateTime
->toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >"de-DE" : "de-DE"
 
     const options = { weekday: "long", year: "numeric", month: "long", day: "numeric" } as const;
@@ -2630,17 +2630,17 @@
 
     zdt.toLocaleString("de-DE", options); // => 'Sonntag, 1. Dezember 2019'
 >zdt.toLocaleString("de-DE", options) : string
->zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >zdt : Temporal.ZonedDateTime
->toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >"de-DE" : "de-DE"
 >options : { readonly weekday: "long"; readonly year: "numeric"; readonly month: "long"; readonly day: "numeric"; }
 
     /* WRONG */ zdt.toLocaleString("de-DE", { timeZone: "Pacific/Auckland" });
 >zdt.toLocaleString("de-DE", { timeZone: "Pacific/Auckland" }) : string
->zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >zdt : Temporal.ZonedDateTime
->toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >"de-DE" : "de-DE"
 >{ timeZone: "Pacific/Auckland" } : { timeZone: string; }
 >timeZone : string
@@ -2649,20 +2649,20 @@
     // => RangeError: Time zone option Pacific/Auckland does not match actual time zone Europe/Berlin
     zdt.withTimeZone("Pacific/Auckland").toLocaleString("de-DE"); // => '2.12.2019, 0:00:00 GMT+13'
 >zdt.withTimeZone("Pacific/Auckland").toLocaleString("de-DE") : string
->zdt.withTimeZone("Pacific/Auckland").toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>zdt.withTimeZone("Pacific/Auckland").toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >zdt.withTimeZone("Pacific/Auckland") : Temporal.ZonedDateTime
 >zdt.withTimeZone : (timeZone: Temporal.TimeZoneLike) => Temporal.ZonedDateTime
 >zdt : Temporal.ZonedDateTime
 >withTimeZone : (timeZone: Temporal.TimeZoneLike) => Temporal.ZonedDateTime
 >"Pacific/Auckland" : "Pacific/Auckland"
->toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >"de-DE" : "de-DE"
 
     zdt.toLocaleString("en-US-u-nu-fullwide-hc-h12"); // => '１２/１/２０１９, １２:００:００ PM GMT+１'
 >zdt.toLocaleString("en-US-u-nu-fullwide-hc-h12") : string
->zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >zdt : Temporal.ZonedDateTime
->toLocaleString : (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions) => string
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
 >"en-US-u-nu-fullwide-hc-h12" : "en-US-u-nu-fullwide-hc-h12"
 }
 
@@ -9126,3 +9126,31 @@
 >plainDateTimeISO : (timeZone?: Temporal.TimeZoneLike) => Temporal.PlainDateTime
 }
 
+{
+    // Refused through a widened variable too, not only in an object literal.
+    const zdt = Temporal.ZonedDateTime.from("2019-12-01T12:00+01:00[Europe/Berlin]");
+>zdt : Temporal.ZonedDateTime
+>Temporal.ZonedDateTime.from("2019-12-01T12:00+01:00[Europe/Berlin]") : Temporal.ZonedDateTime
+>Temporal.ZonedDateTime.from : (item: Temporal.ZonedDateTimeLike, options?: Temporal.ZonedDateTimeFromOptions) => Temporal.ZonedDateTime
+>Temporal.ZonedDateTime : Temporal.ZonedDateTimeConstructor
+>Temporal : typeof Temporal
+>ZonedDateTime : Temporal.ZonedDateTimeConstructor
+>from : (item: Temporal.ZonedDateTimeLike, options?: Temporal.ZonedDateTimeFromOptions) => Temporal.ZonedDateTime
+>"2019-12-01T12:00+01:00[Europe/Berlin]" : "2019-12-01T12:00+01:00[Europe/Berlin]"
+
+    const widened: Intl.DateTimeFormatOptions = { timeZone: "Pacific/Auckland" };
+>widened : Intl.DateTimeFormatOptions
+>Intl : any
+>{ timeZone: "Pacific/Auckland" } : { timeZone: string; }
+>timeZone : string
+>"Pacific/Auckland" : "Pacific/Auckland"
+
+    /* WRONG */ zdt.toLocaleString("de-DE", widened);
+>zdt.toLocaleString("de-DE", widened) : string
+>zdt.toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
+>zdt : Temporal.ZonedDateTime
+>toLocaleString : (locales?: Intl.LocalesArgument, options?: Temporal.ZonedDateTimeToLocaleStringOptions) => string
+>"de-DE" : "de-DE"
+>widened : Intl.DateTimeFormatOptions
+}
+
diff --git a/tsc/testdata/tests/cases/compiler/temporal.ts b/tsc/testdata/tests/cases/compiler/temporal.ts
index e4c4d9472fd2b..d5c0af1887782 100644
--- a/tsc/testdata/tests/cases/compiler/temporal.ts
+++ b/tsc/testdata/tests/cases/compiler/temporal.ts
@@ -1822,3 +1822,10 @@
     Temporal.Now.plainTimeISO(); // get the current wall-clock time in the system time zone and ISO-8601 calendar
     Temporal.Now.plainDateTimeISO(); // same as above, but return the DateTime in the ISO-8601 calendar
 }
+
+{
+    // Refused through a widened variable too, not only in an object literal.
+    const zdt = Temporal.ZonedDateTime.from("2019-12-01T12:00+01:00[Europe/Berlin]");
+    const widened: Intl.DateTimeFormatOptions = { timeZone: "Pacific/Auckland" };
+    /* WRONG */ zdt.toLocaleString("de-DE", widened);
+}