diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index ee604bb0c28..5e0c850008a 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1588,9 +1588,9 @@ declare module 'vscode' {
 
 		/**
 		 * An array of language identifiers that are supported by this
-		 * controller.
+		 * controller. When falsy all languages are supported.
 		 */
-		supportedLanguages: string[];
+		supportedLanguages?: string[];
 
 		/**
 		 * Whether this controller supports execution order so that the
@@ -1636,6 +1636,7 @@ declare module 'vscode' {
 		 */
 		createNotebookCellExecutionTask(cell: NotebookCell): NotebookCellExecutionTask;
 
+		// todo@API find a better name than "preloads"
 		// todo@API allow add, not remove
 		// ipc
 		readonly preloads: NotebookKernelPreload[];
diff --git a/src/vs/workbench/api/common/extHostNotebookKernels.ts b/src/vs/workbench/api/common/extHostNotebookKernels.ts
index 41a4f0fe506..6c5e4473b3c 100644
--- a/src/vs/workbench/api/common/extHostNotebookKernels.ts
+++ b/src/vs/workbench/api/common/extHostNotebookKernels.ts
@@ -124,7 +124,7 @@ export class ExtHostNotebookKernels implements ExtHostNotebookKernelsShape {
 				_update();
 			},
 			get supportedLanguages() {
-				return data.supportedLanguages ?? [];
+				return data.supportedLanguages;
 			},
 			set supportedLanguages(value) {
 				data.supportedLanguages = value;