diff --git a/lib/onelogin/ruby-saml/authrequest.rb b/lib/onelogin/ruby-saml/authrequest.rb
index 732bcdda..78a8f385 100644
--- a/lib/onelogin/ruby-saml/authrequest.rb
+++ b/lib/onelogin/ruby-saml/authrequest.rb
@@ -64,7 +64,7 @@ def create_params(settings, params={})
         request_doc = create_authentication_xml_doc(settings)
         request_doc.context[:attribute_quote] = :quote if settings.double_quote_xml_attribute_values
 
-        request = +""
+        request = "".dup
         request_doc.write(request)
 
         Logging.debug "Created AuthnRequest: #{request}"
diff --git a/lib/onelogin/ruby-saml/logoutrequest.rb b/lib/onelogin/ruby-saml/logoutrequest.rb
index 2508f17a..7ed0766d 100644
--- a/lib/onelogin/ruby-saml/logoutrequest.rb
+++ b/lib/onelogin/ruby-saml/logoutrequest.rb
@@ -61,7 +61,7 @@ def create_params(settings, params={})
         request_doc = create_logout_request_xml_doc(settings)
         request_doc.context[:attribute_quote] = :quote if settings.double_quote_xml_attribute_values
 
-        request = +""
+        request = "".dup
         request_doc.write(request)
 
         Logging.debug "Created SLO Logout Request: #{request}"
diff --git a/lib/onelogin/ruby-saml/metadata.rb b/lib/onelogin/ruby-saml/metadata.rb
index d0f7cba3..a50e9e66 100644
--- a/lib/onelogin/ruby-saml/metadata.rb
+++ b/lib/onelogin/ruby-saml/metadata.rb
@@ -145,7 +145,7 @@ def embed_signature(meta_doc, settings)
       end
 
       def output_xml(meta_doc, pretty_print)
-        ret = +''
+        ret = ''.dup
 
         # pretty print the XML so IdP administrators can easily see what the SP supports
         if pretty_print
diff --git a/lib/onelogin/ruby-saml/slo_logoutresponse.rb b/lib/onelogin/ruby-saml/slo_logoutresponse.rb
index df36d537..9791a73d 100644
--- a/lib/onelogin/ruby-saml/slo_logoutresponse.rb
+++ b/lib/onelogin/ruby-saml/slo_logoutresponse.rb
@@ -70,7 +70,7 @@ def create_params(settings, request_id = nil, logout_message = nil, params = {},
         response_doc = create_logout_response_xml_doc(settings, request_id, logout_message, logout_status_code)
         response_doc.context[:attribute_quote] = :quote if settings.double_quote_xml_attribute_values
 
-        response = +""
+        response = "".dup
         response_doc.write(response)
 
         Logging.debug "Created SLO Logout Response: #{response}"