diff --git a/doc/build.py b/doc/build.py
index 58c9c423..78ada3df 100755
--- a/doc/build.py
+++ b/doc/build.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 # Build the documentation.
 
 from __future__ import print_function