diff --git a/packages/editor/src/utils/media-upload/index.js b/packages/editor/src/utils/media-upload/index.js
index 3edd4fec51d4b..f1f60b7c1e99a 100644
--- a/packages/editor/src/utils/media-upload/index.js
+++ b/packages/editor/src/utils/media-upload/index.js
@@ -31,17 +31,24 @@ export default function mediaUpload( {
 	onError = noop,
 	onFileChange,
 } ) {
-	const { getCurrentPostId, getEditorSettings } = select( editorStore );
+	const { getCurrentPost, getEditorSettings } = select( editorStore );
 	const wpAllowedMimeTypes = getEditorSettings().allowedMimeTypes;
 	maxUploadFileSize =
 		maxUploadFileSize || getEditorSettings().maxUploadFileSize;
-	const currentPostId = getCurrentPostId();
+	const currentPost = getCurrentPost();
+	// Templates and template parts' numerical ID is stored in `wp_id`.
+	const currentPostId =
+		typeof currentPost?.id === 'number'
+			? currentPost.id
+			: currentPost?.wp_id;
+	const postData = currentPostId ? { post: currentPostId } : {};
+
 	uploadMedia( {
 		allowedTypes,
 		filesList,
 		onFileChange,
 		additionalData: {
-			...( ! isNaN( currentPostId ) ? { post: currentPostId } : {} ),
+			...postData,
 			...additionalData,
 		},
 		maxUploadFileSize,