The attached module does not compile and yields the following error: InCoherentInst.hs:17: Could not deduce (Confuse a) from the context (Typeable a) arising from use of `breakFn' at InCoherentInst.hs:17 Probable fix: Add (Confuse a) to the type signature(s) for `addGeneralFallOut' In the first argument of `GeneralBreakFn', namely `breakFn' In the definition of `addGeneralFallOut': addGeneralFallOut = let breakFn a = throwDyn (GeneralFallOutExcep a) in GeneralBreakFn breakFn The same source compiles ok without -fallow-incoherent-instances (or with -fno-allow-incoherent-instances). If, furthermore, the "confusing instance" is commented out, the source even compiles without extensions. I don't know if this is a bug, possibly related to the import of Typeable stuff. I don't need a fix. I only want to point out that globally switching on the option -fallow-incoherent-instances is likely to break existing code, currently (ghc 6.2.2). Cheers Christian