Simon, the commits you pushed today don't validate with -DDEBUG. Unexpected failures: patsyn/should_compile MoreEx [exit code non-0] (normal) patsyn/should_compile T11224b [exit code non-0] (normal) polykinds MonoidsTF [exit code non-0] (normal) polykinds T11480b [exit code non-0] (normal) polykinds T11523 [exit code non-0] (normal) typecheck/should_fail TcCoercibleFail [stderr mismatch] (normal) TcCoercibleFail timed out, and the others all hit the following debug assert: =====> T11224b(normal) 2510 of 5029 [0, 0, 0] Compile failed (status 256) errors were: ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20160218 for x86_64-unknown-linux): ASSERT failed! CallStack (from HasCallStack): assertPprPanic, called at compiler/types/TyCoRep.hs:1932:56 in ghc:TyCoRep checkValidSubst, called at compiler/types/TyCoRep.hs:1991:17 in ghc:TyCoRep substTys, called at compiler/types/TyCoRep.hs:2012:14 in ghc:TyCoRep substTheta, called at compiler/typecheck/TcPatSyn.hs:255:20 in ghc:TcPatSyn in_scope InScope {d_ap0 c_apv} tenv [ap1 :-> c_apv[tau:5]] tenvFVs [aps :-> t_aps[tau:1], apv :-> c_apv[tau:5]] cenv [] cenvFVs [] tys [] cos [] Complete log from Travis: https://s3.amazonaws.com/archive.travis-ci.org/jobs/110115377/log.txt -- Thomas