diff --git a/.rubocop.yml b/.rubocop.yml
index 0c2bb47..cc22ec8 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -15,3 +15,7 @@ Style/SignalException:
 
 Style/SafeNavigation:
   Enabled: false
+
+Style/FileName:
+  Exclude:
+    - gemfiles/Gemfile.*.rb
diff --git a/lib/sensitive_data_filter/middleware.rb b/lib/sensitive_data_filter/middleware.rb
index d39348d..340285a 100644
--- a/lib/sensitive_data_filter/middleware.rb
+++ b/lib/sensitive_data_filter/middleware.rb
@@ -6,7 +6,6 @@ module Middleware
 
 require 'sensitive_data_filter/middleware/env_parser'
 require 'sensitive_data_filter/middleware/parameter_scanner'
-require 'sensitive_data_filter/middleware/parameter_masker'
 require 'sensitive_data_filter/middleware/occurrence'
 require 'sensitive_data_filter/middleware/env_filter'
 require 'sensitive_data_filter/middleware/filter'
diff --git a/lib/sensitive_data_filter/middleware/env_filter.rb b/lib/sensitive_data_filter/middleware/env_filter.rb
index 9e3867f..cf10953 100644
--- a/lib/sensitive_data_filter/middleware/env_filter.rb
+++ b/lib/sensitive_data_filter/middleware/env_filter.rb
@@ -4,11 +4,14 @@
 module SensitiveDataFilter
   module Middleware
     class EnvFilter
+      attr_reader :occurrence
+
       def initialize(env)
-        @env = env
-        @original_env_parser = EnvParser.new env
+        @original_env_parser = EnvParser.new(env)
         @filtered_env_parser = @original_env_parser.copy
-        filter!
+        @scanner             = ParameterScanner.new(@original_env_parser)
+        @filtered_env_parser.mask! if @scanner.sensitive_data?
+        @occurrence = build_occurrence
       end
 
       def filtered_env
@@ -16,23 +19,14 @@ def filtered_env
       end
 
       def occurrence?
-        occurrence.present?
-      end
-
-      def occurrence
-        return nil unless scanner.sensitive_data?
-        @occurrence ||= Occurrence.new(@original_env_parser, @filtered_env_parser, scanner.matches)
+        @occurrence.present?
       end
 
       private
 
-      def filter!
-        return unless scanner.sensitive_data?
-        ParameterMasker.new(@filtered_env_parser).mask!
-      end
-
-      def scanner
-        @scanner ||= ParameterScanner.new @original_env_parser
+      def build_occurrence
+        return nil unless @scanner.sensitive_data?
+        Occurrence.new(@original_env_parser, @filtered_env_parser, @scanner.matches)
       end
     end
   end
diff --git a/lib/sensitive_data_filter/middleware/env_parser.rb b/lib/sensitive_data_filter/middleware/env_parser.rb
index d6bf770..f4266e0 100644
--- a/lib/sensitive_data_filter/middleware/env_parser.rb
+++ b/lib/sensitive_data_filter/middleware/env_parser.rb
@@ -8,37 +8,37 @@ class EnvParser
 
       def initialize(env)
         @env = env
+        @request = Rack::Request.new(@env)
       end
 
       def query_params
-        Rack::Utils.parse_query request.query_string
+        Rack::Utils.parse_query(@request.query_string)
       end
 
       def body_params
-        body = request.body.read
-        request.body.rewind
+        body = @request.body.read
+        @request.body.rewind
         Rack::Utils.parse_query(body)
       end
 
       def query_params=(new_params)
-        @env['QUERY_STRING'] = Rack::Utils.build_query new_params
+        @env['QUERY_STRING'] = Rack::Utils.build_query(new_params)
       end
 
       def body_params=(new_params)
         @env['rack.input'] = StringIO.new Rack::Utils.build_query(new_params)
       end
 
-      def_delegators :request, :ip, :request_method, :url, :params, :session
-
       def copy
         self.class.new(@env.clone)
       end
 
-      private
-
-      def request
-        @request ||= Rack::Request.new @env
+      def mask!
+        self.query_params = SensitiveDataFilter::Mask.mask_hash(query_params)
+        self.body_params  = SensitiveDataFilter::Mask.mask_hash(body_params)
       end
+
+      def_delegators :@request, :ip, :request_method, :url, :params, :session
     end
   end
 end
diff --git a/lib/sensitive_data_filter/middleware/parameter_masker.rb b/lib/sensitive_data_filter/middleware/parameter_masker.rb
deleted file mode 100644
index 7910639..0000000
--- a/lib/sensitive_data_filter/middleware/parameter_masker.rb
+++ /dev/null
@@ -1,15 +0,0 @@
-# frozen_string_literal: true
-module SensitiveDataFilter
-  module Middleware
-    class ParameterMasker
-      def initialize(env_parser)
-        @env_parser = env_parser
-      end
-
-      def mask!
-        @env_parser.query_params = SensitiveDataFilter::Mask.mask_hash @env_parser.query_params
-        @env_parser.body_params  = SensitiveDataFilter::Mask.mask_hash @env_parser.body_params
-      end
-    end
-  end
-end
diff --git a/lib/sensitive_data_filter/middleware/parameter_scanner.rb b/lib/sensitive_data_filter/middleware/parameter_scanner.rb
index 683d8db..4f99c7d 100644
--- a/lib/sensitive_data_filter/middleware/parameter_scanner.rb
+++ b/lib/sensitive_data_filter/middleware/parameter_scanner.rb
@@ -5,22 +5,17 @@ module SensitiveDataFilter
   module Middleware
     class ParameterScanner
       def initialize(env_parser)
-        @env_parser      = env_parser
-        @original_params = @env_parser.query_params.values + @env_parser.body_params.values
+        @env_parser = env_parser
+        @params     = @env_parser.query_params.values + @env_parser.body_params.values
+        @scans      = @params.map { |value| SensitiveDataFilter::Scan.new(value) }
       end
 
       def matches
-        scans.map(&:matches).inject(:collate)
+        @scans.map(&:matches).inject(:collate)
       end
 
       def sensitive_data?
-        scans.any?(&:matches?)
-      end
-
-      private
-
-      def scans
-        @scans ||= @original_params.map { |value| SensitiveDataFilter::Scan.new(value) }
+        @scans.any?(&:matches?)
       end
     end
   end
diff --git a/spec/sensitive_data/middleware/env_filter_spec.rb b/spec/sensitive_data/middleware/env_filter_spec.rb
index e7b56a9..5d82ef1 100644
--- a/spec/sensitive_data/middleware/env_filter_spec.rb
+++ b/spec/sensitive_data/middleware/env_filter_spec.rb
@@ -28,13 +28,11 @@
     allow(env_parser_class).to receive(:new).with(env).and_return env_parser
     allow(env_parser).to receive(:copy).and_return env_parser_copy
 
+    allow(env_parser_copy).to receive(:mask!)
+
     stub_const 'SensitiveDataFilter::Middleware::ParameterScanner', parameter_scanner_class
     allow(parameter_scanner_class).to receive(:new).with(env_parser).and_return parameter_scanner
 
-    stub_const 'SensitiveDataFilter::Middleware::ParameterMasker', parameter_masker_class
-    allow(parameter_masker_class).to receive(:new).with(env_parser_copy).and_return parameter_masker
-    allow(parameter_masker).to receive(:mask!)
-
     stub_const 'SensitiveDataFilter::Middleware::Occurrence', occurrence_class
     allow(occurrence_class)
       .to receive(:new).with(env_parser, env_parser_copy, scan_matches).and_return occurrence
@@ -44,17 +42,15 @@
 
   context 'when sensitive data is detected' do
     let(:sensitive_data?) { true }
-    specify { expect(parameter_masker_class).to have_received(:new).with env_parser_copy }
-    specify { expect(parameter_masker).to have_received :mask! }
+    specify { expect(env_parser_copy).to have_received :mask! }
     specify { expect(env_filter.occurrence?).to be true }
     specify { expect(env_filter.occurrence).to eq occurrence }
     specify { expect(env_filter.filtered_env).to eq filtered_env }
   end
 
-  context 'when sensitive data is detected' do
+  context 'when sensitive data is not detected' do
     let(:sensitive_data?) { false }
-    specify { expect(parameter_masker_class).not_to have_received(:new) }
-    specify { expect(parameter_masker).not_to have_received :mask! }
+    specify { expect(env_parser_copy).not_to have_received :mask! }
     specify { expect(env_filter.occurrence?).to be false }
     specify { expect(env_filter.occurrence).to be_nil }
     specify { expect(env_filter.filtered_env).to eq filtered_env }
diff --git a/spec/sensitive_data/middleware/env_parser_spec.rb b/spec/sensitive_data/middleware/env_parser_spec.rb
index 9fad4db..97e4eb1 100644
--- a/spec/sensitive_data/middleware/env_parser_spec.rb
+++ b/spec/sensitive_data/middleware/env_parser_spec.rb
@@ -57,7 +57,7 @@
   let(:input)  { nil }
 
   # :ip, :request_method, :url, :params
-  context '#ip' do
+  describe '#ip' do
     let(:origin_ip) { '127.0.0.1' }
     before do
       env['REMOTE_ADDR'] = origin_ip
@@ -65,31 +65,31 @@
     specify { expect(env_parser.ip).to eq origin_ip }
   end
 
-  context '#request_method' do
+  describe '#request_method' do
     specify { expect(env_parser.request_method).to eq method }
   end
 
-  context '#url' do
+  describe '#url' do
     specify { expect(env_parser.url).to eq uri }
   end
 
-  context '#params' do
+  describe '#params' do
     specify { expect(env_parser.params).to eq 'id' => '42' }
   end
 
-  context '#session' do
+  describe '#session' do
     before do
       env['rack.session'] = { 'session_id' => '01ab02cd' }
     end
     specify { expect(env_parser.session).to eq 'session_id' => '01ab02cd' }
   end
 
-  context '#copy' do
-    let(:copy) { env_parser.copy }
+  describe '#copy' do
+    let(:masked_env_parser) { env_parser.copy }
 
     before do
-      copy.query_params = { id: 2 }
-      copy.body_params = { test: 2 }
+      masked_env_parser.query_params = { id: 2 }
+      masked_env_parser.body_params = { test: 2 }
 
       env_parser.query_params = { id: 1 }
       env_parser.body_params = { test: 1 }
@@ -98,7 +98,40 @@
     specify { expect(env_parser.query_params).to eq 'id' => '1' }
     specify { expect(env_parser.body_params).to eq 'test' => '1' }
 
-    specify { expect(copy.query_params).to eq 'id' => '2' }
-    specify { expect(copy.body_params).to eq 'test' => '2' }
+    specify { expect(masked_env_parser.query_params).to eq 'id' => '2' }
+    specify { expect(masked_env_parser.body_params).to eq 'test' => '2' }
+  end
+
+  describe '#mask!' do
+    let(:query_params) { { 'sensitive_query' => 'sensitive_data' } }
+    let(:body_params) { { 'sensitive_body' => 'sensitive_data' } }
+
+    before do
+      env_parser.query_params = { sensitive_query: 'sensitive_data' }
+      env_parser.body_params  = { sensitive_body: 'sensitive_data' }
+    end
+
+    context 'before masking' do
+      specify { expect(env_parser.query_params).to eq 'sensitive_query' => 'sensitive_data' }
+      specify { expect(env_parser.body_params).to eq 'sensitive_body' => 'sensitive_data' }
+    end
+
+    context 'after masking' do
+      let(:mask) { double }
+      let(:filtered_query_params) { { 'sensitive_query' => '[FILTERED]' } }
+      let(:filtered_body_params) { { 'sensitive_body' => '[FILTERED]' } }
+
+      before do
+        stub_const 'SensitiveDataFilter::Mask', mask
+        allow(mask).to receive(:mask_hash).with(query_params).and_return filtered_query_params
+        allow(mask).to receive(:mask_hash).with(body_params).and_return filtered_body_params
+        env_parser.mask!
+      end
+
+      specify { expect(mask).to have_received(:mask_hash).with query_params }
+      specify { expect(mask).to have_received(:mask_hash).with body_params }
+      specify { expect(env_parser.query_params).to eq filtered_query_params }
+      specify { expect(env_parser.body_params).to eq filtered_body_params }
+    end
   end
 end
diff --git a/spec/sensitive_data/middleware/occurrence_spec.rb b/spec/sensitive_data/middleware/occurrence_spec.rb
index 09ba99e..1347235 100644
--- a/spec/sensitive_data/middleware/occurrence_spec.rb
+++ b/spec/sensitive_data/middleware/occurrence_spec.rb
@@ -70,7 +70,7 @@
     "Url: https://test.example.com.au/test\n"\
     "Filtered Params: {:credit_cards=>\"[FILTERED] and [FILTERED]\"}\n"\
     "Session: {\"session_id\"=>\"01ab02cd\"}\n"\
-    "Matches Count: {\"CreditCard\"=>2}"
+    'Matches Count: {"CreditCard"=>2}'
   }
 
   specify { expect(occurrence.to_h).to eq expected_to_h }
diff --git a/spec/sensitive_data/middleware/parameter_masker_spec.rb b/spec/sensitive_data/middleware/parameter_masker_spec.rb
deleted file mode 100644
index cc3504d..0000000
--- a/spec/sensitive_data/middleware/parameter_masker_spec.rb
+++ /dev/null
@@ -1,31 +0,0 @@
-# frozen_string_literal: true
-# rubocop:disable Style/BlockDelimiters
-require 'spec_helper'
-
-require 'sensitive_data_filter/middleware/parameter_masker'
-
-describe SensitiveDataFilter::Middleware::ParameterMasker do
-  let(:query_params) { { id: 42 } }
-  let(:body_params) { { credit_card: '4111 1111 1111 1111' } }
-  let(:env_parser) { double query_params: query_params, body_params: body_params }
-  subject(:parameter_masker) { SensitiveDataFilter::Middleware::ParameterMasker.new env_parser }
-
-  describe '#mask!' do
-    let(:mask) { double }
-    let(:filtered_body_params) { { credit_card: '[FILTERED]' } }
-
-    before do
-      stub_const 'SensitiveDataFilter::Mask', mask
-      allow(mask).to receive(:mask_hash).with(query_params).and_return query_params
-      allow(mask).to receive(:mask_hash).with(body_params).and_return filtered_body_params
-
-      allow(env_parser).to receive(:query_params=)
-      allow(env_parser).to receive(:body_params=)
-
-      parameter_masker.mask!
-    end
-
-    specify { expect(env_parser).to have_received(:query_params=).with query_params }
-    specify { expect(env_parser).to have_received(:body_params=).with filtered_body_params }
-  end
-end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 37575a3..870d543 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -2,4 +2,3 @@
 $LOAD_PATH.unshift File.expand_path('../../lib', __FILE__)
 
 require 'support/coverage_loader'
-require 'sensitive_data_filter'
diff --git a/spec/support/coverage_loader.rb b/spec/support/coverage_loader.rb
index 4baff4e..455914b 100644
--- a/spec/support/coverage_loader.rb
+++ b/spec/support/coverage_loader.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 require 'simplecov-rcov'
 require 'coveralls'
 require 'coverage/kit'