diff --git a/tz-format/tz-format-tests.ts b/tz-format/tz-format-tests.ts
index 54e17eeb38..762e78607d 100644
--- a/tz-format/tz-format-tests.ts
+++ b/tz-format/tz-format-tests.ts
@@ -3,4 +3,6 @@
 import * as format from 'tz-format';
 
 format();
+format(1);
 format(new Date());
+format(new Date(), 1);
diff --git a/tz-format/tz-format.d.ts b/tz-format/tz-format.d.ts
index fa8b1c000b..045dc262df 100644
--- a/tz-format/tz-format.d.ts
+++ b/tz-format/tz-format.d.ts
@@ -4,7 +4,7 @@
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 declare module "tz-format" {
-	function format(date?: Date): string;
+	function format(date?: Date | number, offset?: number): string;
 	namespace format { }
 	export = format;
 }