Which match with indentation rule is at play here?

This indentation works fine:

match 5 with
| k when k < 0 ->
  "value is negative"
| k -> "value is non-negative"
|> printfn "%s"

but this does not:

match 5 with
| k when k < 0 ->
  "value is negative"
| k ->
  "value is non-negative"
|> printfn "%s"

Which F# indentation rule is at play?