diff --git a/packages/netlify-cms-core/index.d.ts b/packages/netlify-cms-core/index.d.ts
index f0fdefa4..03a92a77 100644
--- a/packages/netlify-cms-core/index.d.ts
+++ b/packages/netlify-cms-core/index.d.ts
@@ -579,7 +579,7 @@ declare module 'netlify-cms-core' {
     getRemarkPlugins: () => Array<Pluggable>;
     getLocale: (locale: string) => CmsLocalePhrases | undefined;
     getMediaLibrary: (name: string) => CmsMediaLibrary | undefined;
-    selectMediaFiles(field?: EntryField | undefined): MediaFile[];
+    selectMediaFiles: (field?: EntryField | undefined) => MediaFile[];
     resolveWidget: (name: string) => CmsWidget | undefined;
     getPreviewStyles: () => PreviewStyle[];
     getPreviewTemplate: (name: string) => ComponentType<PreviewTemplateComponentProps> | undefined;
diff --git a/packages/netlify-cms-core/src/lib/registry.js b/packages/netlify-cms-core/src/lib/registry.js
index 23f07be8..1ad7c9b0 100644
--- a/packages/netlify-cms-core/src/lib/registry.js
+++ b/packages/netlify-cms-core/src/lib/registry.js
@@ -54,6 +54,7 @@ export default {
   getBackend,
   registerMediaLibrary,
   getMediaLibrary,
+  selectMediaFiles,
   registerLocale,
   getLocale,
   registerEventListener,