diff --git a/api-ref/source/conf.py b/api-ref/source/conf.py
index 88984828c..80973d283 100644
--- a/api-ref/source/conf.py
+++ b/api-ref/source/conf.py
@@ -99,8 +99,8 @@ modindex_common_prefix = ['mistral.']
 # html_last_updated_fmt = '%b %d, %Y'
 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')
 
 # The name for this set of Sphinx documents. If None, it defaults to
 # "<project> v<release> documentation".
diff --git a/doc/source/conf.py b/doc/source/conf.py
index 05e08ad45..67cdf37ce 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -100,8 +100,8 @@ modindex_common_prefix = ['mistral.']
 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".')