diff --git a/doc/source/conf.py b/doc/source/conf.py
index 12d1d4020f..7e4503da96 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -127,8 +127,11 @@ html_static_path = ['_static']
 
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
-git_cmd = "git log --pretty=format:'%ad, commit %h' --date=local -n1"
-html_last_updated_fmt = os.popen(git_cmd).read()
+git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
+   "-n1"]
+html_last_updated_fmt = subprocess.Popen(git_cmd,
+                                         stdout=subprocess.PIPE).\
+                                         communicate()[0]
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.