diff --git a/lib/classes/read-file.js b/lib/classes/read-file.js
index 607c5fe8..54bcf530 100644
--- a/lib/classes/read-file.js
+++ b/lib/classes/read-file.js
@@ -1,11 +1,12 @@
 import { isReadableStream } from "../stream.js";
 
 const ReadFile = class ReadFile {
-	constructor({ mimeType = "", etag = "" } = {}) {
+	constructor({ mimeType = "", etag = "", generation = "" } = {}) {
 		this._mimeType = mimeType;
 		// @ts-ignore
 		this._stream = undefined;
 		this._etag = etag;
+		this._generation = generation;
 	}
 
 	get mimeType() {
@@ -27,6 +28,15 @@ const ReadFile = class ReadFile {
 		return this._etag;
 	}
 
+	/**
+	 * An opaque version token captured at read time. Pass this back to
+	 * sink.write() as options.ifGenerationMatch to perform a compare-and-swap
+	 * write that fails if another writer has modified the file in the meantime.
+	 */
+	get generation() {
+		return this._generation;
+	}
+
 	get [Symbol.toStringTag]() {
 		return "ReadFile";
 	}