diff -up sage-5.10/spkg/build/sage-5.10/module_list.py.orig sage-5.10/spkg/build/sage-5.10/module_list.py --- sage-5.10/spkg/build/sage-5.10/module_list.py.orig 2013-07-29 19:41:05.473022716 -0300 +++ sage-5.10/spkg/build/sage-5.10/module_list.py 2013-07-29 19:41:22.814023380 -0300 @@ -1961,7 +1961,8 @@ ext_modules = [ # These extensions are to be compiled only if the # corresponding packages have been installed -from sage.misc.package import is_package_installed +def is_package_installed(name): + return False if is_package_installed('fes'): ext_modules.extend([