Incorrect error about missing bracket in for await case let loop

[bbrk24]

I got an error about a missing { on line 59 of a file. The relevant excerpt is

/*56*/       var responses: [Int: CalculatedResult] = [:]
/*57*/       for await case let (index, result)? in group {
/*58*/           responses[index] = result
/*59*/       }
/*60*/       return responses

I was initially baffled by the error, but then I figured that maybe it's confused by the for await case let. And indeed, rewriting it to not have that keyword string fixes it -- the following code gives no errors:

            var responses: [Int: CalculatedResult] = [:]
            for await thing in group {
                if let (index, result) = thing {
                    responses[index] = result
                }
            }
            return responses