diff --git a/doc/source/conf.py b/doc/source/conf.py
index edb01f3c39..82935be53b 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -180,8 +180,7 @@ else:
 # using the given strftime format.
 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.