diff --git a/src/vs/workbench/api/browser/mainThreadNotebookDocuments.ts b/src/vs/workbench/api/browser/mainThreadNotebookDocuments.ts
index a406d945ee0..4fbe1ac207f 100644
--- a/src/vs/workbench/api/browser/mainThreadNotebookDocuments.ts
+++ b/src/vs/workbench/api/browser/mainThreadNotebookDocuments.ts
@@ -17,6 +17,7 @@ import { ExtHostContext, ExtHostNotebookShape, IExtHostContext, MainThreadNotebo
 import { MainThreadNotebooksAndEditors } from 'vs/workbench/api/browser/mainThreadNotebookDocumentsAndEditors';
 import { onUnexpectedError } from 'vs/base/common/errors';
 import { Schemas } from 'vs/base/common/network';
+import { NotebookProviderInfo } from 'vs/workbench/contrib/notebook/common/notebookProvider';
 
 export class MainThreadNotebookDocuments implements MainThreadNotebookDocumentsShape {
 
@@ -121,10 +122,16 @@ export class MainThreadNotebookDocuments implements MainThreadNotebookDocumentsS
 
 	async $tryCreateNotebook(options: { viewType: string, content?: NotebookDataDto }): Promise<UriComponents> {
 
+		const info = this._notebookService.getContributedNotebookType(options.viewType);
+		if (!info) {
+			throw new Error('UNKNOWN view type: ' + options.viewType);
+		}
+
 		// find a free URI for the untitled case
+		const suffix = NotebookProviderInfo.possibleFileEnding(info.selectors) ?? '';
 		let uri: URI;
 		for (let counter = 1; ; counter++) {
-			let candidate = URI.from({ scheme: Schemas.untitled, path: `Untitled-${counter}`, query: options.viewType });
+			let candidate = URI.from({ scheme: Schemas.untitled, path: `Untitled-${counter}${suffix}`, query: options.viewType });
 			if (!this._notebookService.getNotebookTextModel(candidate)) {
 				uri = candidate;
 				break;
diff --git a/src/vs/workbench/contrib/notebook/common/notebookProvider.ts b/src/vs/workbench/contrib/notebook/common/notebookProvider.ts
index 7d94ed56c4a..fbdce0aebbd 100644
--- a/src/vs/workbench/contrib/notebook/common/notebookProvider.ts
+++ b/src/vs/workbench/contrib/notebook/common/notebookProvider.ts
@@ -104,4 +104,38 @@ export class NotebookProviderInfo {
 
 		return false;
 	}
+
+	static possibleFileEnding(selectors: NotebookSelector[]): string | undefined {
+		for (let selector of selectors) {
+			const ending = NotebookProviderInfo._possibleFileEnding(selector);
+			if (ending) {
+				return ending;
+			}
+		}
+		return undefined;
+	}
+
+	private static _possibleFileEnding(selector: NotebookSelector): string | undefined {
+
+		const pattern = /^.*(\.[a-zA-Z0-9_-]+)$/;
+
+		let candidate: string | undefined;
+
+		if (typeof selector === 'string') {
+			candidate = selector;
+		} else if (glob.isRelativePattern(selector)) {
+			candidate = selector.pattern;
+		} else if (selector.include) {
+			return NotebookProviderInfo._possibleFileEnding(selector.include);
+		}
+
+		if (candidate) {
+			const match = pattern.exec(candidate);
+			if (match) {
+				return match[1];
+			}
+		}
+
+		return undefined;
+	}
 }