diff --git a/app/server/lib/DocStorageManager.ts b/app/server/lib/DocStorageManager.ts
index 8879db42..7ec65de4 100644
--- a/app/server/lib/DocStorageManager.ts
+++ b/app/server/lib/DocStorageManager.ts
@@ -11,7 +11,7 @@ import * as gutil from 'app/common/gutil';
 import {Comm} from 'app/server/lib/Comm';
 import * as docUtils from 'app/server/lib/docUtils';
 import {GristServer} from 'app/server/lib/GristServer';
-import {IDocStorageManager, SnapshotProgress} from 'app/server/lib/IDocStorageManager';
+import {EmptySnapshotProgress, IDocStorageManager, SnapshotProgress} from 'app/server/lib/IDocStorageManager';
 import {IShell} from 'app/server/lib/IShell';
 import log from 'app/server/lib/log';
 import uuidv4 from "uuid/v4";
@@ -258,14 +258,7 @@ export class DocStorageManager implements IDocStorageManager {
   }
 
   public getSnapshotProgress(): SnapshotProgress {
-    return {
-      pushes: 0,
-      skippedPushes: 0,
-      errors: 0,
-      changes: 0,
-      windowsStarted: 0,
-      windowsDone: 0,
-    };
+    return new EmptySnapshotProgress();
   }
 
   public async replace(docName: string, options: any): Promise<void> {
diff --git a/app/server/lib/HostedStorageManager.ts b/app/server/lib/HostedStorageManager.ts
index fa73beb6..88e5317f 100644
--- a/app/server/lib/HostedStorageManager.ts
+++ b/app/server/lib/HostedStorageManager.ts
@@ -15,7 +15,7 @@ import {IDocWorkerMap} from 'app/server/lib/DocWorkerMap';
 import {ChecksummedExternalStorage, DELETED_TOKEN, ExternalStorage, Unchanged} from 'app/server/lib/ExternalStorage';
 import {HostedMetadataManager} from 'app/server/lib/HostedMetadataManager';
 import {ICreate} from 'app/server/lib/ICreate';
-import {IDocStorageManager, SnapshotProgress} from 'app/server/lib/IDocStorageManager';
+import {EmptySnapshotProgress, IDocStorageManager, SnapshotProgress} from 'app/server/lib/IDocStorageManager';
 import {LogMethods} from "app/server/lib/LogMethods";
 import {fromCallback} from 'app/server/lib/serverUtils';
 import * as fse from 'fs-extra';
@@ -232,14 +232,7 @@ export class HostedStorageManager implements IDocStorageManager {
   public getSnapshotProgress(docName: string): SnapshotProgress {
     let snapshotProgress = this._snapshotProgress.get(docName);
     if (!snapshotProgress) {
-      snapshotProgress = {
-        pushes: 0,
-        skippedPushes: 0,
-        errors: 0,
-        changes: 0,
-        windowsStarted: 0,
-        windowsDone: 0,
-      };
+      snapshotProgress = new EmptySnapshotProgress();
       this._snapshotProgress.set(docName, snapshotProgress);
     }
     return snapshotProgress;
diff --git a/app/server/lib/IDocStorageManager.ts b/app/server/lib/IDocStorageManager.ts
index 6bde92cb..40a1a951 100644
--- a/app/server/lib/IDocStorageManager.ts
+++ b/app/server/lib/IDocStorageManager.ts
@@ -68,7 +68,7 @@ export class TrivialDocStorageManager implements IDocStorageManager {
   public async flushDoc() {}
   public async getSnapshots(): Promise<never> { throw new Error('no'); }
   public async removeSnapshots(): Promise<never> { throw new Error('no'); }
-  public getSnapshotProgress(): SnapshotProgress { throw new Error('no'); }
+  public getSnapshotProgress(): SnapshotProgress { return new EmptySnapshotProgress(); }
   public async replace(): Promise<never> { throw new Error('no'); }
 }
 
@@ -116,3 +116,12 @@ export interface SnapshotProgress {
   /** Number of times a save window was completed. */
   windowsDone: number;
 }
+
+export class EmptySnapshotProgress implements SnapshotProgress {
+  public pushes: number = 0;
+  public skippedPushes: number = 0;
+  public errors: number = 0;
+  public changes: number = 0;
+  public windowsStarted: number = 0;
+  public windowsDone: number = 0;
+}