diff --git a/mach b/mach
index 29ec13f8fde1..16efaa48a7ce 100755
--- a/mach
+++ b/mach
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2.7
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.