diff --git a/api-ref/source/conf.py b/api-ref/source/conf.py
index 34bdfceb8..a0acf4f18 100644
--- a/api-ref/source/conf.py
+++ b/api-ref/source/conf.py
@@ -163,8 +163,7 @@ 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]
+    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 cb0d9e429..5e33300a2 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -188,8 +188,7 @@ html_theme_options = {
 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".')