hcs2hs failure

Is anyone else seeing this in a GHC build utils/hsc2hs/HSCParser.hs:170:14: error: [-Wunused-matches, -Werror=unused-matches] Defined but not used: 'd' | 170 | '\'':d:'\'':_ -> do any3Chars_; text -- Case 2 | ^ Indeed, d looks unused. But this line of code has been there since 28 Dec, so I can't understand why it has not bitten before. With -Werror my build fails. I could switch to -Wwarn, but I think -Werror is the default. Simon