I tried building GHC 6.10.1 with GHC 6.4.2 but failed...

I tried building GHC 6.10.1 with GHC 6.4.2 but failed...

ghc-6.4.2: panic! (the `impossible' happened, GHC version 6.4.2):
        splitTyConApp e1{tv a2p9}

	Please report this as a compiler bug.  See:
	  http://www.haskell.org/ghc/reportabug

<ghc: 38268424 bytes, 8 GCs, 1271792/2445056 avg/max bytes residency (2 samples), 33M in use, 0.01 INIT (0.00 elapsed), 0.52 MUT (2.38 elapsed), 0.07 GC (0.15 elapsed) :ghc>>
gmake[2]: *** [dist-stage1/build/IOEnv.o] Error 1
gmake[1]: *** [build.stage.1] Error 2
gmake: *** [stage1] Error 1