if(NOT LIBPREPROC_IS_EXTERNAL_PROJECT)
  set(LIBPREPROC_PREFIX "" CACHE PATH "The path to the prefix of an libpreproc installation")

  find_path(
    LIBPREPROC_INCLUDE_DIRS
    NAMES preproc/mark.hpp
    PATHS ${LIBPREPROC_PREFIX}/include)
  find_library(
    LIBPREPROC_LIBRARY
    NAMES preproc
    PATHS ${LIBPREPROC_PREFIX}/lib)

  if(LIBPREPROC_INCLUDE_DIRS AND LIBPREPROC_LIBRARY)
    get_filename_component(LIBPREPROC_LIBRARY_DIR ${LIBPREPROC_LIBRARY}
                           DIRECTORY CACHE)
    set(LIBPREPROC_FOUND TRUE)
  endif()

  if(LIBPREPROC_FOUND)
    if(NOT LIBPREPROC_FIND_QUIETLY)
      message(STATUS "Found libpreproc")
    endif()
    set(HAVE_LIBPREPROC 1)
  elseif(LIBPREPROC_FOUND)
    if(LIBPREPROC_FIND_REQUIRED)
      message(FATAL_ERROR "Could not find libpreproc")
    endif()
  endif()
endif()