diff --git a/types/utm/index.d.ts b/types/utm/index.d.ts
index e52f6e01db..22c9f75245 100644
--- a/types/utm/index.d.ts
+++ b/types/utm/index.d.ts
@@ -1,27 +1,40 @@
 // Type definitions for utm 1.1
 // Project: https://github.com/timothygu/utm#readme
 // Definitions by: Hyeonsoo David Lee <https://github.com/civilizeddev>
+//                 Jonas Triki <https://github.com/JonasTriki>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 export function fromLatLon(
-    latitude: number,
-    longitude: number,
-    forceZoneNum?: number,
+  latitude: number,
+  longitude: number,
+  forceZoneNum?: number,
 ): {
-    easting: number
-    northing: number
-    zoneNum: number
-    zoneLetter: string
+  easting: number;
+  northing: number;
+  zoneNum: number;
+  zoneLetter: string;
 };
 
 export function toLatLon(
-    easting: number,
-    northing: number,
-    zoneNum: number,
-    zoneLetter: string,
-    northern: boolean,
-    strict?: boolean,
+  easting: number,
+  northing: number,
+  zoneNum: number,
+  zoneLetter: string,
+  northern?: undefined,
+  strict?: boolean,
 ): {
-    latitude: number
-    longitude: number
+  latitude: number;
+  longitude: number;
+};
+
+export function toLatLon(
+  easting: number,
+  northing: number,
+  zoneNum: number,
+  zoneLetter: undefined,
+  northern: boolean,
+  strict?: boolean,
+): {
+  latitude: number;
+  longitude: number;
 };
diff --git a/types/utm/utm-tests.ts b/types/utm/utm-tests.ts
index 10b3a984f6..b89938d980 100644
--- a/types/utm/utm-tests.ts
+++ b/types/utm/utm-tests.ts
@@ -8,11 +8,10 @@ const latLon1 = {
 const utmCoord1 = fromLatLon(latLon1.lat, latLon1.lon);
 
 const latLon2 = toLatLon(
-    utmCoord1.easting,
-    utmCoord1.northing,
-    utmCoord1.zoneNum,
-    utmCoord1.zoneLetter,
-    true,
+  utmCoord1.easting,
+  utmCoord1.northing,
+  utmCoord1.zoneNum,
+  utmCoord1.zoneLetter,
 );
 
 const utmCoord2 = fromLatLon(latLon2.latitude, latLon2.longitude);