diff --git a/types/luxon/index.d.ts b/types/luxon/index.d.ts
index b5f1134fb5..eebf89497d 100644
--- a/types/luxon/index.d.ts
+++ b/types/luxon/index.d.ts
@@ -1,4 +1,4 @@
-// Type definitions for luxon 1.10
+// Type definitions for luxon 1.11
 // Project: https://github.com/moment/luxon#readme
 // Definitions by: Colby DeHart <https://github.com/colbydehart>
 //                 Hyeonseok Yang <https://github.com/FourwingsY>
@@ -436,7 +436,7 @@ export class Interval {
     splitAt(...dateTimes: DateTime[]): Interval[];
     splitBy(duration: Duration | DurationObject | number): Interval[];
     toDuration(
-        unit: DurationUnit | DurationUnit[],
+        unit?: DurationUnit | DurationUnit[],
         options?: DiffOptions
     ): Duration;
     toFormat(
diff --git a/types/luxon/luxon-tests.ts b/types/luxon/luxon-tests.ts
index df5481094b..59566c35c3 100644
--- a/types/luxon/luxon-tests.ts
+++ b/types/luxon/luxon-tests.ts
@@ -144,6 +144,7 @@ i.mapEndpoints((d) => d); // $ExpectType Interval
 i.toISO(); // $ExpectType string
 i.toString(); // $ExpectType string
 i.toDuration('months'); // $ExpectType Duration
+i.toDuration(); // $ExpectType Duration
 
 if (Interval.isInterval(anything)) {
     anything; // $ExpectType Interval