diff --git a/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts b/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts
index 2f773b8436c..5381bc67978 100644
--- a/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts
+++ b/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts
@@ -68,9 +68,9 @@ const kernel1 = new class implements vscode.NotebookKernel {
 			}
 
 			task.start();
-			await task.replaceOutput([new vscode.NotebookCellOutput([
+			await task.replaceOutput(new vscode.NotebookCellOutput([
 				new vscode.NotebookCellOutputItem('text/plain', ['my output'], undefined)
-			])]);
+			]));
 			task.end({ success: true });
 			return;
 		}
diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 3fd5e086bd6..407f4ad13b4 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1573,8 +1573,8 @@ declare module 'vscode' {
 		readonly token: CancellationToken;
 
 		clearOutput(cellIndex?: number): Thenable<void>;
-		appendOutput(out: NotebookCellOutput[], cellIndex?: number): Thenable<void>;
-		replaceOutput(out: NotebookCellOutput[], cellIndex?: number): Thenable<void>;
+		appendOutput(out: NotebookCellOutput | NotebookCellOutput[], cellIndex?: number): Thenable<void>;
+		replaceOutput(out: NotebookCellOutput | NotebookCellOutput[], cellIndex?: number): Thenable<void>;
 		appendOutputItems(items: NotebookCellOutputItem[], outputId: string): Thenable<void>;
 		replaceOutputItems(items: NotebookCellOutputItem[], outputId: string): Thenable<void>;
 	}
diff --git a/src/vs/workbench/api/common/extHostNotebook.ts b/src/vs/workbench/api/common/extHostNotebook.ts
index d06967d37ea..30c639ad64f 100644
--- a/src/vs/workbench/api/common/extHostNotebook.ts
+++ b/src/vs/workbench/api/common/extHostNotebook.ts
@@ -1164,23 +1164,25 @@ class NotebookCellExecutionTask extends Disposable {
 				return this.replaceOutput([], cellIndex);
 			},
 
-			async appendOutput(outputs: vscode.NotebookCellOutput[], cellIndex?: number): Promise<void> {
+			async appendOutput(outputs: vscode.NotebookCellOutput | vscode.NotebookCellOutput[], cellIndex?: number): Promise<void> {
 				that.verifyStateForOutput();
 				const handle = that.cellIndexToHandle(cellIndex);
 				if (typeof handle !== 'number') {
 					return;
 				}
 
+				outputs = Array.isArray(outputs) ? outputs : [outputs];
 				return that.applyEdits([{ editType: CellEditType.Output, handle, append: true, outputs: outputs.map(typeConverters.NotebookCellOutput.from) }]);
 			},
 
-			async replaceOutput(outputs: vscode.NotebookCellOutput[], cellIndex?: number): Promise<void> {
+			async replaceOutput(outputs: vscode.NotebookCellOutput | vscode.NotebookCellOutput[], cellIndex?: number): Promise<void> {
 				that.verifyStateForOutput();
 				const handle = that.cellIndexToHandle(cellIndex);
 				if (typeof handle !== 'number') {
 					return;
 				}
 
+				outputs = Array.isArray(outputs) ? outputs : [outputs];
 				return that.applyEdits([{ editType: CellEditType.Output, handle, outputs: outputs.map(typeConverters.NotebookCellOutput.from) }]);
 			},