diff --git a/src/vs/platform/files/common/files.ts b/src/vs/platform/files/common/files.ts
index 04788f62ec1..c625aad7a66 100644
--- a/src/vs/platform/files/common/files.ts
+++ b/src/vs/platform/files/common/files.ts
@@ -399,9 +399,9 @@ export interface IFileChange {
 
 export class FileChangesEvent {
 
-	private _changes: IFileChange[];
+	private readonly _changes: readonly IFileChange[];
 
-	constructor(changes: IFileChange[]) {
+	constructor(changes: readonly IFileChange[]) {
 		this._changes = changes;
 	}
 
diff --git a/src/vs/platform/files/test/node/diskFileService.test.ts b/src/vs/platform/files/test/node/diskFileService.test.ts
index 238ccd8ede7..3f5c57ec1a8 100644
--- a/src/vs/platform/files/test/node/diskFileService.test.ts
+++ b/src/vs/platform/files/test/node/diskFileService.test.ts
@@ -1918,7 +1918,7 @@ suite('Disk File Service', function () {
 		});
 	}
 
-	function hasChange(changes: IFileChange[], type: FileChangeType, resource: URI): boolean {
+	function hasChange(changes: readonly IFileChange[], type: FileChangeType, resource: URI): boolean {
 		return changes.some(change => change.type === type && isEqual(change.resource, resource));
 	}