I'm getting this with "sh validate -legacy" compiler/main/DynFlags.hs:1344:15: error: [-Woverlapping-patterns, -Werror=overlapping-patterns] Pattern match is redundant In an equation for 'settings': settings s | otherwise = ... | 1344 | | otherwise = panic $ "Invalid cfg parameters." ++ exampleString | ^^^^^^^^^ This is when compiling the stage-2 compiler. There's an ifdef in DynFlags thus #if __GLASGOW_HASKELL__ <= 810 | otherwise = panic $ "Invalid cfg parameters." ++ exampleString #endif but somehow it's not triggering for the stage2 compiler. Any ideas? It's blocking a full build. This #ifdef was added in 8038cbd96f4, when GHC became better at reporting redundant code. Simon