diff --git a/api-ref/source/conf.py b/api-ref/source/conf.py
index 3a3cb5099d..26917f6b3b 100644
--- a/api-ref/source/conf.py
+++ b/api-ref/source/conf.py
@@ -166,8 +166,7 @@ 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 d651ec87f2..19f6e9dac6 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -212,8 +212,7 @@ html_static_path = ['_static']
 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".')