diff --git a/var/spack/repos/builtin/packages/lmod/package.py b/var/spack/repos/builtin/packages/lmod/package.py
index 9084c3488120fa566256e6d9fb6da39732f224cf..e50c2cfc4bf7a20d2c71034574a9b55e56126e3d 100644
--- a/var/spack/repos/builtin/packages/lmod/package.py
+++ b/var/spack/repos/builtin/packages/lmod/package.py
@@ -23,7 +23,7 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 from spack import *
-import os
+
 
 class Lmod(Package):
     """
@@ -38,13 +38,19 @@ class Lmod(Package):
     url = 'https://github.com/TACC/Lmod/archive/6.4.1.tar.gz'
 
     version('6.4.1', '7978ba777c8aa41a4d8c05fec5f780f4')
-    version('6.3.7', '0fa4d5a24c41cae03776f781aa2dedc1', preferred=True)
+    version('6.3.7', '0fa4d5a24c41cae03776f781aa2dedc1')
     version('6.0.1', '91abf52fe5033bd419ffe2842ebe7af9')
 
     depends_on('lua@5.2:')
     depends_on('lua-luaposix')
     depends_on('lua-luafilesystem')
 
+    parallel = False
+
+    def setup_environment(self, spack_env, run_env):
+        stage_lua_path = join_path(self.stage.path, 'Lmod-{version}', 'src', '?.lua')
+        spack_env.append_path('LUA_PATH', stage_lua_path.format(version=self.version), separator=';')
+
     def install(self, spec, prefix):
         configure('--prefix=%s' % prefix)
         make('install')