I have a program that's using both json (0.4.4) and hslogger (1.1.0). During the "cabal configure" stage of compiling my program, I get this error message: Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package json-0.4.4 requires mtl-1.1.0.2 package hslogger-1.1.0 requires mtl-2.0.1.0 Looking at the .cabal files for json and hslogger, they both have dependencies on "mtl", but neither package gives a version for it. I only have mtl 2.0.1.0 installed, so installing json didn't bring in an old version of the library when it was installed. My program compiles and runs without any errors. Can anybody tell my why cabal thinks json needs mtl 1.1.0.2, and what I can do to make the message go away?