diff --git a/lib/http/cookie.rb b/lib/http/cookie.rb
index 5e5ee98..493472a 100644
--- a/lib/http/cookie.rb
+++ b/lib/http/cookie.rb
@@ -413,6 +413,7 @@ class HTTP::Cookie
 
   # See #origin.
   def origin=(origin)
+    return origin if origin == @origin
     @origin.nil? or
       raise ArgumentError, "origin cannot be changed once it is set"
     origin = URI(origin)