diff --git a/lib/saml/base.rb b/lib/saml/base.rb
index 8fb147c..541c32b 100644
--- a/lib/saml/base.rb
+++ b/lib/saml/base.rb
@@ -42,10 +42,6 @@ def use_original(object)
 
     module XmlMapperClassMethods
       def parse(xml, options = {})
-        if xml.is_a?(String)
-          ActiveSupport::XmlMini_REXML.parse(xml)
-        end
-
         object = super
         if object.is_a?(Array)
           object.map { |x| x.from_xml = true }
@@ -53,7 +49,7 @@ def parse(xml, options = {})
           object.from_xml = true
         end
         object
-      rescue Nokogiri::XML::SyntaxError, REXML::ParseException => e
+      rescue Nokogiri::XML::SyntaxError => e
         raise Saml::Errors::UnparseableMessage.new(e.message)
       rescue TypeError => e
         raise Saml::Errors::UnparseableMessage.new(e.message)
diff --git a/saml.gemspec b/saml.gemspec
index a06977d..e5961fd 100644
--- a/saml.gemspec
+++ b/saml.gemspec
@@ -19,8 +19,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'activesupport', '>= 4.2'
   s.add_dependency 'activemodel', '>= 4.2'
   s.add_dependency 'xmlmapper', '~> 0.8.1'
-  s.add_dependency 'nokogiri', '~> 1.11'
-  s.add_dependency 'rexml'
+  s.add_dependency 'nokogiri', '>= 1.11.4', '< 2.0'
   s.add_dependency 'xmldsig', '>= 0.5.1', '< 0.8.0'
   s.add_dependency 'xmlenc', '>= 0.6.9', '< 0.9.0'
 
diff --git a/spec/lib/saml/base_spec.rb b/spec/lib/saml/base_spec.rb
index 72e316a..bf9d9f7 100644
--- a/spec/lib/saml/base_spec.rb
+++ b/spec/lib/saml/base_spec.rb
@@ -36,8 +36,8 @@ class BaseDummy
 <samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" IssueInstant="2013-08-25T14:31:07Z" AssertionConsumerServiceURL="test:&lol4;"></samlp:AuthnRequest>
       XML
 
-      it 'raises an Saml::Errors::HackAttack for entity expansion has grown too large' do
-        expect { BaseDummy.parse(xml) }.to raise_error RuntimeError, 'entity expansion has grown too large'
+      it 'raises a Saml::Errors::UnparseableMessage instead of expanding the entities' do
+        expect { BaseDummy.parse(xml) }.to raise_error(Saml::Errors::UnparseableMessage)
       end
     end
 
@@ -58,7 +58,7 @@ class BaseDummy
     end
 
     it 'raises an error when a method does not exist' do
-      expect(ActiveSupport::XmlMini_REXML).to receive(:parse).and_raise(NoMethodError)
+      expect(Nokogiri).to receive(:XML).and_raise(NoMethodError)
       expect {
         BaseDummy.parse('unknown')
       }.to raise_error(Saml::Errors::UnparseableMessage)
diff --git a/spec/lib/saml/complex_types/request_abstract_type_spec.rb b/spec/lib/saml/complex_types/request_abstract_type_spec.rb
index 11f5aac..a3dbcab 100644
--- a/spec/lib/saml/complex_types/request_abstract_type_spec.rb
+++ b/spec/lib/saml/complex_types/request_abstract_type_spec.rb
@@ -82,14 +82,17 @@
               wsa_address:    'address'
           }
       )
-      xml = Hash.from_xml(soap)
-      expect(xml["Envelope"]["Header"]).to eq(
-                                           "MessageID" => "id",
-                                           "To"        => "to",
-                                           "Action"    => "some_action",
-                                           "ReplyTo"   => { "Address" => "address" },
-                                           'xmlns:wsa' => 'http://schemas.xmlsoap.org/ws/2004/08/addressing'
-                                       )
+      namespaces = {
+          'soapenv' => 'http://schemas.xmlsoap.org/soap/envelope/',
+          'wsa'     => 'http://schemas.xmlsoap.org/ws/2004/08/addressing'
+      }
+      header = Nokogiri::XML::Document.parse(soap).at_xpath('//soapenv:Header', namespaces)
+
+      expect(header.namespaces['xmlns:wsa']).to eq('http://schemas.xmlsoap.org/ws/2004/08/addressing')
+      expect(header.at_xpath('wsa:MessageID', namespaces).text).to eq('id')
+      expect(header.at_xpath('wsa:To', namespaces).text).to eq('to')
+      expect(header.at_xpath('wsa:Action', namespaces).text).to eq('some_action')
+      expect(header.at_xpath('wsa:ReplyTo/wsa:Address', namespaces).text).to eq('address')
     end
   end