diff --git a/lib/savon.rb b/lib/savon.rb
index ea0fe365..b8ece228 100644
--- a/lib/savon.rb
+++ b/lib/savon.rb
@@ -26,3 +26,4 @@ def self.notify_observers(operation_name, builder, globals, locals)
 require "savon/version"
 require "savon/client"
 require "savon/model"
+require "savon/string_utils"
diff --git a/lib/savon/builder.rb b/lib/savon/builder.rb
index e2c905b6..454c6f4f 100644
--- a/lib/savon/builder.rb
+++ b/lib/savon/builder.rb
@@ -163,7 +163,7 @@ def serialized_messages
       message_tag = serialized_message_tag[1]
       @wsdl.soap_input(@operation_name.to_sym)[message_tag].each_pair do |message, type|
         break if @locals[:message].nil?
-        message_locals = @locals[:message][message.snakecase.to_sym]
+        message_locals = @locals[:message][StringUtils.snakecase(message).to_sym]
         message_content = Message.new(message_tag, namespace_identifier, @types, @used_namespaces, message_locals, :unqualified, @globals[:convert_request_keys_to], @globals[:unwrap]).to_s
         messages += "<#{message} xsi:type=\"#{type.join(':')}\">#{message_content}</#{message}>"
       end
diff --git a/lib/savon/core_ext/string.rb b/lib/savon/core_ext/string.rb
deleted file mode 100644
index 292afb33..00000000
--- a/lib/savon/core_ext/string.rb
+++ /dev/null
@@ -1,30 +0,0 @@
-# frozen_string_literal: true
-
-module Savon
-  module CoreExt
-    module String
-
-      def self.included(base)
-        unless "savon".respond_to?(:snakecase)
-          base.send(:include, Extension)
-        end
-      end
-
-      module Extension
-        def snakecase
-          str = dup
-          str.gsub! /::/, '/'
-          str.gsub! /([A-Z]+)([A-Z][a-z])/, '\1_\2'
-          str.gsub! /([a-z\d])([A-Z])/, '\1_\2'
-          str.tr! ".", "_"
-          str.tr! "-", "_"
-          str.downcase!
-          str
-        end
-      end
-
-    end
-  end
-end
-
-String.send :include, Savon::CoreExt::String
diff --git a/lib/savon/model.rb b/lib/savon/model.rb
index 58937f47..a44debc6 100644
--- a/lib/savon/model.rb
+++ b/lib/savon/model.rb
@@ -29,7 +29,7 @@ def all_operations
     # Defines a class-level SOAP operation.
     def define_class_operation(operation)
       class_operation_module.module_eval %{
-        def #{operation.to_s.snakecase}(locals = {})
+        def #{StringUtils.snakecase(operation.to_s)}(locals = {})
           client.call #{operation.inspect}, locals
         end
       }
@@ -38,8 +38,8 @@ def #{operation.to_s.snakecase}(locals = {})
     # Defines an instance-level SOAP operation.
     def define_instance_operation(operation)
       instance_operation_module.module_eval %{
-        def #{operation.to_s.snakecase}(locals = {})
-          self.class.#{operation.to_s.snakecase} locals
+        def #{StringUtils.snakecase(operation.to_s)}(locals = {})
+          self.class.#{StringUtils.snakecase(operation.to_s)} locals
         end
       }
     end
diff --git a/lib/savon/options.rb b/lib/savon/options.rb
index 55004aee..71d78666 100644
--- a/lib/savon/options.rb
+++ b/lib/savon/options.rb
@@ -85,7 +85,7 @@ def initialize(options = {})
         :raise_errors                => true,
         :strip_namespaces            => true,
         :delete_namespace_attributes => false,
-        :convert_response_tags_to    => lambda { |tag| tag.snakecase.to_sym},
+        :convert_response_tags_to    => lambda { |tag| StringUtils.snakecase(tag).to_sym},
         :convert_attributes_to       => lambda { |k,v| [k,v] },
         :multipart                   => false,
         :adapter                     => nil,
diff --git a/lib/savon/string_utils.rb b/lib/savon/string_utils.rb
new file mode 100644
index 00000000..f6d9f88b
--- /dev/null
+++ b/lib/savon/string_utils.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module Savon
+  module StringUtils
+    def self.snakecase(inputstring)
+      str = inputstring.dup
+      str.gsub! /::/, '/'
+      str.gsub! /([A-Z]+)([A-Z][a-z])/, '\1_\2'
+      str.gsub! /([a-z\d])([A-Z])/, '\1_\2'
+      str.tr! ".", "_"
+      str.tr! "-", "_"
+      str.downcase!
+      str
+    end
+  end
+end
+
diff --git a/spec/savon/core_ext/string_spec.rb b/spec/savon/core_ext/string_spec.rb
deleted file mode 100644
index 54f658b5..00000000
--- a/spec/savon/core_ext/string_spec.rb
+++ /dev/null
@@ -1,38 +0,0 @@
-# frozen_string_literal: true
-require "spec_helper"
-
-RSpec.describe String do
-
-  describe "snakecase" do
-    it "lowercases one word CamelCase" do
-      expect("Merb".snakecase).to eq("merb")
-    end
-
-    it "makes one underscore snakecase two word CamelCase" do
-      expect("MerbCore".snakecase).to eq("merb_core")
-    end
-
-    it "handles CamelCase with more than 2 words" do
-      expect("SoYouWantContributeToMerbCore".snakecase).to eq("so_you_want_contribute_to_merb_core")
-    end
-
-    it "handles CamelCase with more than 2 capital letter in a row" do
-      expect("CNN".snakecase).to eq("cnn")
-      expect("CNNNews".snakecase).to eq("cnn_news")
-      expect("HeadlineCNNNews".snakecase).to eq("headline_cnn_news")
-    end
-
-    it "does NOT change one word lowercase" do
-      expect("merb".snakecase).to eq("merb")
-    end
-
-    it "leaves snake_case as is" do
-      expect("merb_core".snakecase).to eq("merb_core")
-    end
-
-    it "converts period characters to underscores" do
-      expect("User.GetEmail".snakecase).to eq("user_get_email")
-    end
-  end
-
-end
diff --git a/spec/savon/options_spec.rb b/spec/savon/options_spec.rb
index 247df12e..914d3be4 100644
--- a/spec/savon/options_spec.rb
+++ b/spec/savon/options_spec.rb
@@ -844,7 +844,7 @@ def to_s
     it "can be changed to not strip any namespaces" do
       client = new_client(
         :endpoint => @server.url(:repeat),
-        :convert_response_tags_to => lambda { |tag| tag.snakecase },
+        :convert_response_tags_to => lambda { |tag| Savon::StringUtils.snakecase(tag) },
         :strip_namespaces => false
       )
 
@@ -877,7 +877,7 @@ def to_s
 
   context "global :convert_response_tags_to" do
     it "changes how XML tags from the SOAP response are translated into Hash keys" do
-      client = new_client(:endpoint => @server.url(:repeat), :convert_response_tags_to => lambda { |tag| tag.snakecase.upcase })
+      client = new_client(:endpoint => @server.url(:repeat), :convert_response_tags_to => lambda { |tag| Savon::StringUtils.snakecase(tag).upcase })
       response = client.call(:authenticate, :xml => Fixture.response(:authentication))
 
       expect(response.full_hash["ENVELOPE"]["BODY"]).to include("AUTHENTICATE_RESPONSE")
@@ -888,7 +888,7 @@ def to_s
         globals.log                      false
         globals.wsdl                     Fixture.wsdl(:authentication)
         globals.endpoint                 @server.url(:repeat)
-        globals.convert_response_tags_to { |tag| tag.snakecase.upcase }
+        globals.convert_response_tags_to { |tag| Savon::StringUtils.snakecase(tag).upcase }
       end
 
       response = client.call(:authenticate) do |locals|
@@ -1115,7 +1115,7 @@ def to_s
 
   context "request :response_parser" do
     it "instructs Nori to change the response parser" do
-      nori = Nori.new(:strip_namespaces => true, :convert_tags_to => lambda { |tag| tag.snakecase.to_sym })
+      nori = Nori.new(:strip_namespaces => true, :convert_tags_to => lambda { |tag| Savon::StringUtils.snakecase(tag).to_sym })
       Nori.expects(:new).with { |options| options[:parser] == :nokogiri }.returns(nori)
 
       client = new_client(:endpoint => @server.url(:repeat))
diff --git a/spec/savon/soap_fault_spec.rb b/spec/savon/soap_fault_spec.rb
index d66ab935..1dde0501 100644
--- a/spec/savon/soap_fault_spec.rb
+++ b/spec/savon/soap_fault_spec.rb
@@ -12,7 +12,7 @@
   let(:soap_fault_no_body) { Savon::SOAPFault.new new_response(:body => {}), nori }
   let(:no_fault) { Savon::SOAPFault.new new_response, nori }
 
-  let(:nori) { Nori.new(:strip_namespaces => true, :convert_tags_to => lambda { |tag| tag.snakecase.to_sym }) }
+  let(:nori) { Nori.new(:strip_namespaces => true, :convert_tags_to => lambda { |tag| Savon::StringUtils.snakecase(tag).to_sym }) }
   let(:nori_no_convert) { Nori.new(:strip_namespaces => true, :convert_tags_to => nil) }
 
   it "inherits from Savon::Error" do
diff --git a/spec/savon/string_utils_spec.rb b/spec/savon/string_utils_spec.rb
new file mode 100644
index 00000000..1055ea3d
--- /dev/null
+++ b/spec/savon/string_utils_spec.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+require "spec_helper"
+
+RSpec.describe Savon::StringUtils do
+
+  describe "snakecase" do
+    it "lowercases one word CamelCase" do
+      expect(Savon::StringUtils.snakecase("Merb")).to eq("merb")
+    end
+
+    it "makes one underscore snakecase two word CamelCase" do
+      expect(Savon::StringUtils.snakecase("MerbCore")).to eq("merb_core")
+    end
+
+    it "handles CamelCase with more than 2 words" do
+      expect(Savon::StringUtils.snakecase("SoYouWantContributeToMerbCore")).to eq("so_you_want_contribute_to_merb_core")
+    end
+
+    it "handles CamelCase with more than 2 capital letter in a row" do
+      expect(Savon::StringUtils.snakecase("CNN")).to eq("cnn")
+      expect(Savon::StringUtils.snakecase("CNNNews")).to eq("cnn_news")
+      expect(Savon::StringUtils.snakecase("HeadlineCNNNews")).to eq("headline_cnn_news")
+    end
+
+    it "does NOT change one word lowercase" do
+      expect(Savon::StringUtils.snakecase("merb")).to eq("merb")
+    end
+
+    it "leaves snake_case as is" do
+      expect(Savon::StringUtils.snakecase("merb_core")).to eq("merb_core")
+    end
+
+    it "converts period characters to underscores" do
+      expect(Savon::StringUtils.snakecase("User.GetEmail")).to eq("user_get_email")
+    end
+  end
+
+end
diff --git a/spec/support/fixture.rb b/spec/support/fixture.rb
index a4777c5a..a30b060a 100644
--- a/spec/support/fixture.rb
+++ b/spec/support/fixture.rb
@@ -21,7 +21,7 @@ def full_hash(fixture)
   private
 
     def nori
-      Nori.new(:strip_namespaces => true, :convert_tags_to => lambda { |tag| tag.snakecase.to_sym })
+      Nori.new(:strip_namespaces => true, :convert_tags_to => lambda { |tag| Savon::StringUtils.snakecase(tag).to_sym })
     end
 
     def fixtures(type)