diff --git a/src/types/core/api.d.ts b/src/types/core/api.d.ts
index 4f9f73d2ffb..b0694bff5ba 100644
--- a/src/types/core/api.d.ts
+++ b/src/types/core/api.d.ts
@@ -284,7 +284,7 @@ export function prependTraces(
 /** Render the plot to a data URI or SVG string. */
 export function toImage(root: RootOrData, opts?: ToImgopts): Promise<string>;
 /** Render the plot and trigger a browser download. */
-export function downloadImage(root: RootOrData, opts: DownloadImgopts): Promise<string>;
+export function downloadImage(root: RootOrData, opts?: DownloadImgopts): Promise<string>;
 
 /**
  * Reconcile the plot's current state with the supplied figure. Comparable