My environment's TEMP and TMP are C:\temp, but for some reason, my recent Cygwin install makes 'TEMP' and 'TMP' /cygdrive/c/temp/4; this duly gets passed to ghc-inplace as C:\temp\4. Then, in libraries\base, ghc-split complains that \4 mentions a non-existent group in a regexp: ../../ghc/compiler/ghc-inplace -H16m -O -fglasgow-exts -cpp -Iinclude -#include HsBase.h -Icbits/regex -funbox-strict-fields -package-name base -O -Rghc-timing -split-objs -c GHC/Base.lhs -o GHC/Base.o -ohi GHC/Base.hi Reference to nonexistent group in regex; marked by <-- HERE in m/"c:\temp\4 <--HERE \ghc936.split\.c"/ at d:\\users\\cooney\\ghc\\ghc-6.0\ghc\driver\split\ghc-split line 51, <TMPI> line 23. make[2]: *** [GHC/Base.o] Error 255 All I needed to do was editing ghc\driver\split\ghc-split so $Tmp_prefix = $ARGV[1] was instead ($Tmp_prefix = $ARGV[1]) =~ s/\\/\\\\/g; I don't know whether this habit of appending \4 is a delightful quirk of my Cygwin install, but FWIW for other Windows Server 2k3/Cygwin users out there... Dominic Cooney