`deno check` error: Cannot find name 'Deno'`

In my project, deno checkdeno check has started producing the error TS2304 [ERROR]: Cannot find name 'Deno'TS2304 [ERROR]: Cannot find name 'Deno' . I've found a lot of reports about this error coming from the VS Code extension, but in my case it's coming from Deno itself, and the VS Code extension does NOT show this problem. I'm quite confused! Can anybody suggest a solution please?