diff --git a/bin/spack b/bin/spack
index 081c76ca21..3cb3c7f423 100755
--- a/bin/spack
+++ b/bin/spack
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2.7
 
 import os
 import sys
diff --git a/lib/spack/spack/test/test_versions.py b/lib/spack/spack/test/test_versions.py
index ecf98c2dbb..e8a2295c1e 100755
--- a/lib/spack/spack/test/test_versions.py
+++ b/lib/spack/spack/test/test_versions.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2.7
 """\
 This file has a bunch of versions tests taken from the excellent version
 detection in Homebrew.