diff --git a/var/spack/packages/boost/package.py b/var/spack/packages/boost/package.py
index 9b7c22c53d9..3427b74ad68 100644
--- a/var/spack/packages/boost/package.py
+++ b/var/spack/packages/boost/package.py
@@ -95,11 +95,11 @@ def determine_bootstrap_options(self, spec, options):
         with open('user-config.jam', 'w') as f:
             if '+mpi' in spec:
                 f.write('using mpi : %s ;\n' %
-                    joinpath(spec['mpi'].prefix.bin, 'mpicxx'))
+                    join_path(spec['mpi'].prefix.bin, 'mpicxx'))
             if '+python' in spec:
                 f.write('using python : %s : %s ;\n' %
                     (spec['python'].version,
-                    joinpath(spec['python'].prefix.bin, 'python')))
+                    join_path(spec['python'].prefix.bin, 'python')))
 
     def determine_b2_options(self, spec, options):
         if '+debug' in spec: