diff --git a/src/vs/workbench/contrib/notebook/browser/contrib/coreActions.ts b/src/vs/workbench/contrib/notebook/browser/contrib/coreActions.ts
index 6c92f48da49..2b264acf741 100644
--- a/src/vs/workbench/contrib/notebook/browser/contrib/coreActions.ts
+++ b/src/vs/workbench/contrib/notebook/browser/contrib/coreActions.ts
@@ -1650,7 +1650,7 @@ registerAction2(class ChangeCellLanguageAction extends NotebookCellAction<ICellR
 
 	private async setLanguage(context: IChangeCellContext, languageId: string) {
 		if (languageId === 'markdown' && context.cell?.language !== 'markdown') {
-			const newCell = await changeCellToKind(CellKind.Markup, { cell: context.cell, notebookEditor: context.notebookEditor }, 'markdown');
+			const newCell = await changeCellToKind(CellKind.Markup, { cell: context.cell, notebookEditor: context.notebookEditor }, 'markdown', Mimes.markdown);
 			if (newCell) {
 				context.notebookEditor.focusNotebookCell(newCell, 'editor');
 			}