The most recent libmad release does not use pkgconfig, and while some distributors have gone ahead and provided a .pc file, not all have. This fixes it for the non-pkgconfig case. Index: flow/gsl/CMakeLists.txt =================================================================== --- flow/gsl/CMakeLists.txt (revision 1242076) +++ flow/gsl/CMakeLists.txt (working copy) @@ -63,7 +63,11 @@ if( MAD_FOUND ) set( GSL_HAVE_LIBMAD 1 ) else( MAD_FOUND ) - message(FATAL_ERROR "\nMAD support are requested, but `libmad` not found" ) + find_library( MAD_LIBRARIES NAMES mad ) + find_path( MAD_INCLUDE_DIRS mad.h ) + if( NOT MAD_LIBRARIES ) + message(FATAL_ERROR "\nMAD support is requested, but `libmad` not found" ) + endif( NOT MAD_LIBRARIES ) endif( MAD_FOUND ) endif( WITH_MAD )