diff --git a/index.d.ts b/index.d.ts
index 2abdfa16b9..dcdfa9eb4b 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -714,13 +714,13 @@ declare namespace dashjs {
 
         getSuggestedPresentationDelay(): string;
 
-        getAvailabilityStartTime(externalManifest: object): number;
+        getAvailabilityStartTime(externalManifest?: object): number;
 
-        getIsDynamic(externalManifest: object): boolean;
+        getIsDynamic(externalManifest?: object): boolean;
 
-        getDuration(externalManifest: object): number;
+        getDuration(externalManifest?: object): number;
 
-        getRegularPeriods(externalManifest: object): any[];
+        getRegularPeriods(externalManifest?: object): any[];
 
         getMpd(externalManifest?: object): Mpd;