--- a/process/factory.py
+++ b/process/factory.py
@@ -2944,17 +2944,17 @@ class BaseRepackFactory(MozillaBuildFact
         if self.callClientPy:
             self.addClientPySteps()
 
     def addClientPySteps(self):
         c = self.clientPyConfig
 
         # build up the checkout command with all options
         skipBlankRepos = c.get('skip_blank_repos', False)
-        co_command = ['python', 'client.py', 'checkout']
+        co_command = ['python2.7', 'client.py', 'checkout']
         if c.get('moz_repo_path'):
             co_command.append('--mozilla-repo=%s' %
                               self.getRepository(c.get('moz_repo_path')))
         if c.get('inspector_repo_path'):
             co_command.append('--inspector-repo=%s' % self.getRepository(
                 c.get('inspector_repo_path')))
         elif skipBlankRepos:
             co_command.append('--skip-inspector')