diff --git a/layouts/_default/baseof.html b/layouts/_default/baseof.html
index e112b64..9a83951 100644
--- a/layouts/_default/baseof.html
+++ b/layouts/_default/baseof.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<html lang="{{- default "" .Site.LanguageCode -}}">
+<html lang="{{- default "" .Site.LanguageCode -}}" prefix="og: http://ogp.me/ns#">
 {{- partial "head.html" . -}}
 {{- partial "header.html" . -}}
 <main id="content">
