diff --git a/_includes/seo.html b/_includes/seo.html
index ca66e4df..4223fb19 100644
--- a/_includes/seo.html
+++ b/_includes/seo.html
@@ -41,7 +41,7 @@
 
 <meta name="author" content="{{ seo_author }}">
 
-<meta property="og:locale" content="{{ site.locale | replace: "-", "_" | default: "en" }}">
+<meta property="og:locale" content="{{ site.locale | replace: "-", "_" | default: "en_US" }}">
 <meta property="og:site_name" content="{{ site.title }}">
 <meta property="og:title" content="{{ page.title | default: site.title | markdownify | strip_html | strip_newlines | escape_once }}">
 
diff --git a/docs/_includes/seo.html b/docs/_includes/seo.html
index ca66e4df..4223fb19 100644
--- a/docs/_includes/seo.html
+++ b/docs/_includes/seo.html
@@ -41,7 +41,7 @@
 
 <meta name="author" content="{{ seo_author }}">
 
-<meta property="og:locale" content="{{ site.locale | replace: "-", "_" | default: "en" }}">
+<meta property="og:locale" content="{{ site.locale | replace: "-", "_" | default: "en_US" }}">
 <meta property="og:site_name" content="{{ site.title }}">
 <meta property="og:title" content="{{ page.title | default: site.title | markdownify | strip_html | strip_newlines | escape_once }}">