diff --git a/lib/rack/request.rb b/lib/rack/request.rb
index c28e33c19..40922a219 100644
--- a/lib/rack/request.rb
+++ b/lib/rack/request.rb
@@ -497,7 +497,7 @@ def GET
       # multipart/form-data.
       def POST
         if error = get_header(RACK_REQUEST_FORM_ERROR)
-          raise error.class, error.message, cause: error
+          raise error.class, error.message, cause: error.cause
         end
 
         begin