diff --git a/actionpack/lib/action_controller/templates/rescues/layout.erb b/actionpack/lib/action_controller/templates/rescues/layout.erb
index d38f3e67f9..4a04742e40 100644
--- a/actionpack/lib/action_controller/templates/rescues/layout.erb
+++ b/actionpack/lib/action_controller/templates/rescues/layout.erb
@@ -1,4 +1,4 @@
-<html>
+<html xmlns="http://www.w3.org/1999/xhtml">
 <head>
   <title>Action Controller: Exception caught</title>
   <style>
