diff --git a/api-ref/source/conf.py b/api-ref/source/conf.py
index edf5622c35b..900cbb622f9 100644
--- a/api-ref/source/conf.py
+++ b/api-ref/source/conf.py
@@ -159,10 +159,9 @@ html_theme_options = {
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
 # html_last_updated_fmt = '%b %d, %Y'
-git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
+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]
+html_last_updated_fmt = subprocess.check_output(git_cmd).decode('utf-8')
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.
diff --git a/doc/source/conf.py b/doc/source/conf.py
index f47fc2fee87..b295921d8e3 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -195,11 +195,10 @@ html_static_path = ['_static']
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
 # html_last_updated_fmt = '%b %d, %Y'
-git_cmd = ["git", "log", "--pretty=format:'%ad, commit %h'", "--date=local",
+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".')