diff --git a/activesupport/lib/active_support/xml_mini/libxml.rb b/activesupport/lib/active_support/xml_mini/libxml.rb
index 7fdcb11465..16570c6aea 100644
--- a/activesupport/lib/active_support/xml_mini/libxml.rb
+++ b/activesupport/lib/active_support/xml_mini/libxml.rb
@@ -1,5 +1,6 @@
 require 'libxml'
 require 'active_support/core_ext/object/blank'
+require 'stringio'
 
 # = XmlMini LibXML implementation
 module ActiveSupport
diff --git a/activesupport/lib/active_support/xml_mini/libxmlsax.rb b/activesupport/lib/active_support/xml_mini/libxmlsax.rb
index fe2c1b9349..2536b1f33e 100644
--- a/activesupport/lib/active_support/xml_mini/libxmlsax.rb
+++ b/activesupport/lib/active_support/xml_mini/libxmlsax.rb
@@ -1,5 +1,6 @@
 require 'libxml'
 require 'active_support/core_ext/object/blank'
+require 'stringio'
 
 # = XmlMini LibXML implementation using a SAX-based parser
 module ActiveSupport
@@ -82,4 +83,4 @@ module ActiveSupport
       end
     end
   end
-end
\ No newline at end of file
+end
diff --git a/activesupport/lib/active_support/xml_mini/nokogiri.rb b/activesupport/lib/active_support/xml_mini/nokogiri.rb
index e03a744257..04ec9e8ab8 100644
--- a/activesupport/lib/active_support/xml_mini/nokogiri.rb
+++ b/activesupport/lib/active_support/xml_mini/nokogiri.rb
@@ -5,6 +5,7 @@ rescue LoadError => e
   raise e
 end
 require 'active_support/core_ext/object/blank'
+require 'stringio'
 
 # = XmlMini Nokogiri implementation
 module ActiveSupport
diff --git a/activesupport/lib/active_support/xml_mini/nokogirisax.rb b/activesupport/lib/active_support/xml_mini/nokogirisax.rb
index 25afbfcd1c..93fd3dfe57 100644
--- a/activesupport/lib/active_support/xml_mini/nokogirisax.rb
+++ b/activesupport/lib/active_support/xml_mini/nokogirisax.rb
@@ -5,6 +5,7 @@ rescue LoadError => e
   raise e
 end
 require 'active_support/core_ext/object/blank'
+require 'stringio'
 
 # = XmlMini Nokogiri implementation using a SAX-based parser
 module ActiveSupport
diff --git a/activesupport/lib/active_support/xml_mini/rexml.rb b/activesupport/lib/active_support/xml_mini/rexml.rb
index 36692af1d3..a13ad10118 100644
--- a/activesupport/lib/active_support/xml_mini/rexml.rb
+++ b/activesupport/lib/active_support/xml_mini/rexml.rb
@@ -1,5 +1,6 @@
 require 'active_support/core_ext/kernel/reporting'
 require 'active_support/core_ext/object/blank'
+require 'stringio'
 
 # = XmlMini ReXML implementation
 module ActiveSupport