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 20:07:59.033084505 -0300 +++ sage-5.10/spkg/build/sage-5.10/module_list.py 2013-07-29 20:08:09.815084918 -0300 @@ -1966,7 +1966,7 @@ ext_modules = [ def is_package_installed(name): return False -if is_package_installed('fes'): +if 1: ext_modules.extend([ Extension("sage.libs.fes", ["sage/libs/fes.pyx"],