--- a/modules/toplevel/manifests/slave/releng.pp
+++ b/modules/toplevel/manifests/slave/releng.pp
@@ -10,16 +10,20 @@ class toplevel::slave::releng inherits t
     include instance_metadata
     include clean::appstate
 
     # packages common to all slaves
     include packages::mozilla::tooltool
     include packages::wget
     include packages::mozilla::py27_mercurial
 
+    if ($::operatingsystem == Darwin) {
+        include packages::mozilla::py27_virtualenv
+    }
+
     if ($::operatingsystem == Windows) {
         include tweaks::memory_paging
         include tweaks::nouac
         include tweaks::ntfs_options
         include tweaks::process_priority
         include tweaks::pwrshell_options
         include tweaks::server_initialize
         include tweaks::windows_network_opt_netsh