diff --git a/src/vs/workbench/api/common/extHostNotebook.ts b/src/vs/workbench/api/common/extHostNotebook.ts
index 510a24cf4a3..e7956730308 100644
--- a/src/vs/workbench/api/common/extHostNotebook.ts
+++ b/src/vs/workbench/api/common/extHostNotebook.ts
@@ -358,11 +358,19 @@ export class ExtHostNotebookController implements ExtHostNotebookShape {
 		if (!serializer) {
 			throw new Error('NO serializer found');
 		}
+
 		const data = await serializer.deserializeNotebook(bytes.buffer, token);
-		return {
+		const res: NotebookDataDto = {
 			metadata: typeConverters.NotebookDocumentMetadata.from(data.metadata),
-			cells: data.cells.map(typeConverters.NotebookCellData.from),
+			cells: [],
 		};
+
+		for (let cell of data.cells) {
+			extHostTypes.NotebookCellData.validate(cell);
+			res.cells.push(typeConverters.NotebookCellData.from(cell));
+		}
+
+		return res;
 	}
 
 	async $notebookToData(handle: number, data: NotebookDataDto, token: CancellationToken): Promise<VSBuffer> {
diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index e2105622baa..d6464b14833 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -3023,6 +3023,18 @@ export class NotebookDocumentMetadata {
 
 export class NotebookCellData {
 
+	static validate(data: NotebookCellData): void {
+		if (typeof data.kind !== 'number') {
+			throw new Error('NotebookCellData MUST have \'kind\' property');
+		}
+		if (typeof data.value !== 'string') {
+			throw new Error('NotebookCellData MUST have \'value\' property');
+		}
+		if (typeof data.languageId !== 'string') {
+			throw new Error('NotebookCellData MUST have \'languageId\' property');
+		}
+	}
+
 	static isNotebookCellDataArray(value: unknown): value is vscode.NotebookCellData[] {
 		return Array.isArray(value) && (<unknown[]>value).every(elem => NotebookCellData.isNotebookCellData(elem));
 	}
@@ -3046,6 +3058,8 @@ export class NotebookCellData {
 		this.outputs = outputs ?? [];
 		this.metadata = metadata;
 		this.latestExecutionSummary = latestExecutionSummary;
+
+		NotebookCellData.validate(this);
 	}
 }