diff --git a/api-ref/source/conf.py b/api-ref/source/conf.py
index 5d50ae16..777355fb 100644
--- a/api-ref/source/conf.py
+++ b/api-ref/source/conf.py
@@ -157,8 +157,7 @@ pygments_style = 'sphinx'
 git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
     "-n1"]
 try:
-    html_last_updated_fmt = subprocess.Popen(
-        git_cmd, stdout=subprocess.PIPE).communicate()[0].decode()
+    html_last_updated_fmt = subprocess.check_output(git_cmd).decode('utf-8')
 except Exception:
     warnings.warn('Cannot get last updated time from git repository. '
                   'Not setting "html_last_updated_fmt".')
diff --git a/doc/source/conf.py b/doc/source/conf.py
index d670c647..8a4c8fb7 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -65,8 +65,7 @@ htmlhelp_basename = '%sdoc' % project
 git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
     "-n1"]
 try:
-    html_last_updated_fmt = subprocess.Popen(
-        git_cmd, stdout=subprocess.PIPE).communicate()[0]
+    html_last_updated_fmt = subprocess.check_output(git_cmd).decode('utf-8')
 except Exception:
     warnings.warn('Cannot get last updated time from git repository. '
                   'Not setting "html_last_updated_fmt".')