diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index b25973d0cb05880851de4d2359d52d7ecb98e378..0c534c0dbe65d8b5f449ee6ca610f747b66117eb 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1671,6 +1671,7 @@ declare module 'vscode' {
 	}
 
 	export interface NotebookConcatTextDocument {
+		onDidChange: Event<void>;
 		version: number;
 		getText(): string;
 		getText(range: Range): string;
diff --git a/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts b/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
index fc86657861c74efce8f5532b6c88261d9ef383a2..60e87eca7268fe07e10985afd72965555fb8eb37 100644
--- a/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
+++ b/src/vs/workbench/api/common/extHostNotebookConcatDocument.ts
@@ -23,8 +23,8 @@ export class ExtHostNotebookConcatDocument implements vscode.NotebookConcatTextD
 	private _cellLines!: PrefixSumComputer;
 	private _versionId = 0;
 
-	private readonly _onDidChange = new Emitter<this>();
-	readonly onDidChange: Event<this> = this._onDidChange.event;
+	private readonly _onDidChange = new Emitter<void>();
+	readonly onDidChange: Event<void> = this._onDidChange.event;
 
 	constructor(
 		extHostNotebooks: ExtHostNotebookController,
@@ -40,14 +40,14 @@ export class ExtHostNotebookConcatDocument implements vscode.NotebookConcatTextD
 				this._cellLengths.changeValue(cellIdx, this._cells[cellIdx].document.getText().length + 1);
 				this._cellLines.changeValue(cellIdx, this._cells[cellIdx].document.lineCount);
 				this._versionId += 1;
-				this._onDidChange.fire(this);
+				this._onDidChange.fire(undefined);
 			}
 		}));
 		this._disposables.add(extHostNotebooks.onDidChangeNotebookDocument(e => {
 			if (e.document === this._notebook) {
 				this._init();
 				this._versionId += 1;
-				this._onDidChange.fire(this);
+				this._onDidChange.fire(undefined);
 			}
 		}));
 	}