diff --git a/src/vs/workbench/api/browser/mainThreadWebview.ts b/src/vs/workbench/api/browser/mainThreadWebview.ts
index ee94a7b2007d4081a7d0321cc0de78c332e8ede0..0db614fa9bcbff2a53c5354a7e25069623c6f282 100644
--- a/src/vs/workbench/api/browser/mainThreadWebview.ts
+++ b/src/vs/workbench/api/browser/mainThreadWebview.ts
@@ -795,6 +795,7 @@ class MainThreadCustomEditorModel extends Disposable implements ICustomEditorMod
 			return undefined;
 		}
 		// TODO: handle save untitled case
+		// TODO: handle cancellation
 		await createCancelablePromise(token => this._proxy.$onSave(this._editorResource, this.viewType, token));
 		this.change(() => {
 			this._savePoint = this._currentEditIndex;
@@ -804,7 +805,8 @@ class MainThreadCustomEditorModel extends Disposable implements ICustomEditorMod
 
 	public async saveCustomEditorAs(resource: URI, targetResource: URI, _options?: ISaveOptions): Promise<boolean> {
 		if (this._editable) {
-			await this._proxy.$onSaveAs(this._editorResource, this.viewType, targetResource);
+			// TODO: handle cancellation
+			await createCancelablePromise(token => this._proxy.$onSaveAs(this._editorResource, this.viewType, targetResource, token));
 			this.change(() => {
 				this._savePoint = this._currentEditIndex;
 			});
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index c64dbcef8d95e9718fa747a667f0132042e90be6..08822c2e01bc4cd15115c7f0d43e8f6da1617ef6 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -649,7 +649,7 @@ export interface ExtHostWebviewsShape {
 	$disposeEdits(resourceComponents: UriComponents, viewType: string, editIds: number[]): void;
 
 	$onSave(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void>;
-	$onSaveAs(resource: UriComponents, viewType: string, targetResource: UriComponents): Promise<void>;
+	$onSaveAs(resource: UriComponents, viewType: string, targetResource: UriComponents, cancellation: CancellationToken): Promise<void>;
 
 	$backup(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void>;
 
diff --git a/src/vs/workbench/api/common/extHostWebview.ts b/src/vs/workbench/api/common/extHostWebview.ts
index aced97ccc25ebbbaa3093cf6a06e7c35f58911c7..fdcf7623620eaa9afb3fc22c782515cfdb23eb41 100644
--- a/src/vs/workbench/api/common/extHostWebview.ts
+++ b/src/vs/workbench/api/common/extHostWebview.ts
@@ -630,10 +630,10 @@ export class ExtHostWebviews implements extHostProtocol.ExtHostWebviewsShape {
 		return delegate.save(document, cancellation);
 	}
 
-	async $onSaveAs(resourceComponents: UriComponents, viewType: string, targetResource: UriComponents): Promise<void> {
+	async $onSaveAs(resourceComponents: UriComponents, viewType: string, targetResource: UriComponents, cancellation: CancellationToken): Promise<void> {
 		const delegate = this.getEditingDelegate(viewType);
 		const document = this.getCustomDocument(viewType, resourceComponents);
-		return delegate.saveAs(document, URI.revive(targetResource));
+		return delegate.saveAs(document, URI.revive(targetResource), cancellation);
 	}
 
 	async $backup(resourceComponents: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void> {