diff --git a/lib/api.d.ts b/lib/api.d.ts
index 5c4c89a..cae77bb 100644
--- a/lib/api.d.ts
+++ b/lib/api.d.ts
@@ -11,7 +11,7 @@ export class Application {
     constructor(resourceFileURL: URL | string, instantiate: any, argv0: string);
 
     run(args: string[], files: Tree, options: {
-        printLine: (line: string) => void,
-        decodeASCII: boolean
+        printLine?: (line: string) => void,
+        decodeASCII?: boolean
     }): Promise<Tree>;
 }