diff --git a/types/js-yaml/index.d.ts b/types/js-yaml/index.d.ts
index 8f7c0a346d..892320cc7c 100644
--- a/types/js-yaml/index.d.ts
+++ b/types/js-yaml/index.d.ts
@@ -18,8 +18,8 @@ declare namespace jsyaml {
 		public static create(schemas: Schema[] | Schema, types: Type[] | Type): Schema;
 	}
 
-	export function safeLoadAll(str: string, iterator: (doc: any) => void, opts?: LoadOptions): any;
-	export function loadAll(str: string, iterator: (doc: any) => void, opts?: LoadOptions): any;
+	export function safeLoadAll(str: string, iterator?: (doc: any) => void, opts?: LoadOptions): any;
+	export function loadAll(str: string, iterator?: (doc: any) => void, opts?: LoadOptions): any;
 
 	export function safeDump(obj: any, opts?: DumpOptions): string;
 	export function dump(obj: any, opts?: DumpOptions): string;