diff --git a/lib/rexml/source.rb b/lib/rexml/source.rb
index 9a9b8f5d..655164f3 100644
--- a/lib/rexml/source.rb
+++ b/lib/rexml/source.rb
@@ -1,6 +1,7 @@
 # coding: US-ASCII
 # frozen_string_literal: false
 
+require "stringio"
 require "strscan"
 
 require_relative 'encoding'
@@ -45,7 +46,6 @@ def SourceFactory::create_from(arg)
           arg.respond_to? :eof?
         IOSource.new(arg)
       elsif arg.respond_to? :to_str
-        require 'stringio'
         IOSource.new(StringIO.new(arg))
       elsif arg.kind_of? Source
         arg