diff --git a/lib/grape/dsl/inside_route.rb b/lib/grape/dsl/inside_route.rb
index e2bc9169ad..cc56a72d21 100644
--- a/lib/grape/dsl/inside_route.rb
+++ b/lib/grape/dsl/inside_route.rb
@@ -224,9 +224,9 @@ def status(status = nil)
       # Set response content-type
       def content_type(val = nil)
         if val
-          header(Grape::Http::Headers::CONTENT_TYPE, val)
+          header(Rack::CONTENT_TYPE, val)
         else
-          header[Grape::Http::Headers::CONTENT_TYPE]
+          header[Rack::CONTENT_TYPE]
         end
       end
 
@@ -328,9 +328,9 @@ def sendfile(value = nil)
       def stream(value = nil)
         return if value.nil? && @stream.nil?
 
-        header Grape::Http::Headers::CONTENT_LENGTH, nil
-        header Grape::Http::Headers::TRANSFER_ENCODING, nil
-        header Grape::Http::Headers::CACHE_CONTROL, 'no-cache' # Skips ETag generation (reading the response up front)
+        header Rack::CONTENT_LENGTH, nil
+        header Rack::TRANSFER_ENCODING, nil
+        header Rack::CACHE_CONTROL, 'no-cache' # Skips ETag generation (reading the response up front)
         if value.is_a?(String)
           file_body = Grape::ServeStream::FileBody.new(value)
           @stream = Grape::ServeStream::StreamResponse.new(file_body)
diff --git a/lib/grape/http/headers.rb b/lib/grape/http/headers.rb
index eb6a1c3ff0..a9cd7d1ee5 100644
--- a/lib/grape/http/headers.rb
+++ b/lib/grape/http/headers.rb
@@ -12,21 +12,13 @@ module Headers
       QUERY_STRING    = 'QUERY_STRING'
 
       if Grape.lowercase_headers?
-        ALLOW             = 'allow'
-        CACHE_CONTROL     = 'cache-control'
-        CONTENT_LENGTH    = 'content-length'
-        CONTENT_TYPE      = 'content-type'
-        LOCATION          = 'location'
-        TRANSFER_ENCODING = 'transfer-encoding'
-        X_CASCADE         = 'x-cascade'
+        ALLOW     = 'allow'
+        LOCATION  = 'location'
+        X_CASCADE = 'x-cascade'
       else
-        ALLOW             = 'Allow'
-        CACHE_CONTROL     = 'Cache-Control'
-        CONTENT_LENGTH    = 'Content-Length'
-        CONTENT_TYPE      = 'Content-Type'
-        LOCATION          = 'Location'
-        TRANSFER_ENCODING = 'Transfer-Encoding'
-        X_CASCADE         = 'X-Cascade'
+        ALLOW     = 'Allow'
+        LOCATION  = 'Location'
+        X_CASCADE = 'X-Cascade'
       end
 
       GET     = 'GET'
diff --git a/lib/grape/middleware/error.rb b/lib/grape/middleware/error.rb
index 259d610eb4..05fc0312f2 100644
--- a/lib/grape/middleware/error.rb
+++ b/lib/grape/middleware/error.rb
@@ -51,7 +51,7 @@ def call!(env)
       end
 
       def error!(message, status = options[:default_status], headers = {}, backtrace = [], original_exception = nil)
-        headers = headers.reverse_merge(Grape::Http::Headers::CONTENT_TYPE => content_type)
+        headers = headers.reverse_merge(Rack::CONTENT_TYPE => content_type)
         rack_response(format_message(message, backtrace, original_exception), status, headers)
       end
 
@@ -63,15 +63,15 @@ def default_rescue_handler(e)
       def error_response(error = {})
         status = error[:status] || options[:default_status]
         message = error[:message] || options[:default_message]
-        headers = { Grape::Http::Headers::CONTENT_TYPE => content_type }
+        headers = { Rack::CONTENT_TYPE => content_type }
         headers.merge!(error[:headers]) if error[:headers].is_a?(Hash)
         backtrace = error[:backtrace] || error[:original_exception]&.backtrace || []
         original_exception = error.is_a?(Exception) ? error : error[:original_exception] || nil
         rack_response(format_message(message, backtrace, original_exception), status, headers)
       end
 
-      def rack_response(message, status = options[:default_status], headers = { Grape::Http::Headers::CONTENT_TYPE => content_type })
-        message = ERB::Util.html_escape(message) if headers[Grape::Http::Headers::CONTENT_TYPE] == TEXT_HTML
+      def rack_response(message, status = options[:default_status], headers = { Rack::CONTENT_TYPE => content_type })
+        message = ERB::Util.html_escape(message) if headers[Rack::CONTENT_TYPE] == TEXT_HTML
         Rack::Response.new([message], Rack::Utils.status_code(status), headers)
       end
 
diff --git a/lib/grape/middleware/formatter.rb b/lib/grape/middleware/formatter.rb
index 06d9a4931d..0f8e7cdb3c 100644
--- a/lib/grape/middleware/formatter.rb
+++ b/lib/grape/middleware/formatter.rb
@@ -54,7 +54,7 @@ def build_formatted_response(status, headers, bodies)
       end
 
       def fetch_formatter(headers, options)
-        api_format = mime_types[headers[Grape::Http::Headers::CONTENT_TYPE]] || env[Grape::Env::API_FORMAT]
+        api_format = mime_types[headers[Rack::CONTENT_TYPE]] || env[Grape::Env::API_FORMAT]
         Grape::Formatter.formatter_for(api_format, **options)
       end
 
@@ -63,10 +63,10 @@ def fetch_formatter(headers, options)
       # @param headers [Hash]
       # @return [Hash]
       def ensure_content_type(headers)
-        if headers[Grape::Http::Headers::CONTENT_TYPE]
+        if headers[Rack::CONTENT_TYPE]
           headers
         else
-          headers.merge(Grape::Http::Headers::CONTENT_TYPE => content_type_for(env[Grape::Env::API_FORMAT]))
+          headers.merge(Rack::CONTENT_TYPE => content_type_for(env[Grape::Env::API_FORMAT]))
         end
       end
 
diff --git a/spec/grape/api_spec.rb b/spec/grape/api_spec.rb
index 5e31f51cfc..39dc9df4d4 100644
--- a/spec/grape/api_spec.rb
+++ b/spec/grape/api_spec.rb
@@ -689,7 +689,7 @@ class DummyFormatClass
         'example'
       end
       put '/example'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eql 'text/plain'
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eql 'text/plain'
     end
 
     describe 'adds an OPTIONS route that' do
@@ -1196,32 +1196,32 @@ class DummyFormatClass
 
     it 'sets content type for txt format' do
       get '/foo'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('text/plain')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('text/plain')
     end
 
     it 'does not set Cache-Control' do
       get '/foo'
-      expect(last_response.headers[Grape::Http::Headers::CACHE_CONTROL]).to be_nil
+      expect(last_response.headers[Rack::CACHE_CONTROL]).to be_nil
     end
 
     it 'sets content type for xml' do
       get '/foo.xml'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('application/xml')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('application/xml')
     end
 
     it 'sets content type for json' do
       get '/foo.json'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('application/json')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('application/json')
     end
 
     it 'sets content type for serializable hash format' do
       get '/foo.serializable_hash'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('application/json')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('application/json')
     end
 
     it 'sets content type for binary format' do
       get '/foo.binary'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('application/octet-stream')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('application/octet-stream')
     end
 
     it 'returns raw data when content type binary' do
@@ -1230,7 +1230,7 @@ class DummyFormatClass
       subject.format :binary
       subject.get('/binary_file') { File.binread(image_filename) }
       get '/binary_file'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('application/octet-stream')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('application/octet-stream')
       expect(last_response.body).to eq(file)
     end
 
@@ -1242,8 +1242,8 @@ class DummyFormatClass
 
       subject.get('/file') { file test_file }
       get '/file'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_LENGTH]).to eq('25')
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('text/plain')
+      expect(last_response.headers[Rack::CONTENT_LENGTH]).to eq('25')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('text/plain')
       expect(last_response.body).to eq(file_content)
     end
 
@@ -1257,10 +1257,10 @@ class DummyFormatClass
       subject.get('/stream') { stream test_stream }
       get '/stream', {}, 'HTTP_VERSION' => 'HTTP/1.1', 'SERVER_PROTOCOL' => 'HTTP/1.1'
 
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('text/plain')
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_LENGTH]).to be_nil
-      expect(last_response.headers[Grape::Http::Headers::CACHE_CONTROL]).to eq('no-cache')
-      expect(last_response.headers[Grape::Http::Headers::TRANSFER_ENCODING]).to eq('chunked')
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('text/plain')
+      expect(last_response.headers[Rack::CONTENT_LENGTH]).to be_nil
+      expect(last_response.headers[Rack::CACHE_CONTROL]).to eq('no-cache')
+      expect(last_response.headers[Rack::TRANSFER_ENCODING]).to eq('chunked')
 
       expect(last_response.body).to eq("c\r\nThis is some\r\nd\r\n file content\r\n0\r\n\r\n")
     end
@@ -1268,7 +1268,7 @@ class DummyFormatClass
     it 'sets content type for error' do
       subject.get('/error') { error!('error in plain text', 500) }
       get '/error'
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eql 'text/plain'
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eql 'text/plain'
     end
 
     it 'sets content type for json error' do
@@ -1276,7 +1276,7 @@ class DummyFormatClass
       subject.get('/error') { error!('error in json', 500) }
       get '/error.json'
       expect(last_response.status).to be 500
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eql 'application/json'
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eql 'application/json'
     end
 
     it 'sets content type for xml error' do
@@ -1284,7 +1284,7 @@ class DummyFormatClass
       subject.get('/error') { error!('error in xml', 500) }
       get '/error'
       expect(last_response.status).to be 500
-      expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eql 'application/xml'
+      expect(last_response.headers[Rack::CONTENT_TYPE]).to eql 'application/xml'
     end
 
     it 'includes extension in format' do
@@ -1314,12 +1314,12 @@ class DummyFormatClass
 
       it 'sets content type' do
         get '/custom.custom'
-        expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eql 'application/custom'
+        expect(last_response.headers[Rack::CONTENT_TYPE]).to eql 'application/custom'
       end
 
       it 'sets content type for error' do
         get '/error.custom'
-        expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eql 'application/custom'
+        expect(last_response.headers[Rack::CONTENT_TYPE]).to eql 'application/custom'
       end
     end
 
@@ -1339,7 +1339,7 @@ class DummyFormatClass
           image_filename = 'grape.png'
           post url, file: Rack::Test::UploadedFile.new(image_filename, 'image/png', true)
           expect(last_response.status).to eq(201)
-          expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('image/png')
+          expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('image/png')
           expect(last_response.headers['Content-Disposition']).to eq("attachment; filename*=UTF-8''grape.png")
           File.open(image_filename, 'rb') do |io|
             expect(last_response.body).to eq io.read
@@ -1351,7 +1351,7 @@ class DummyFormatClass
         filename = __FILE__
         post '/attachment.rb', file: Rack::Test::UploadedFile.new(filename, 'application/x-ruby', true)
         expect(last_response.status).to eq(201)
-        expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq('application/x-ruby')
+        expect(last_response.headers[Rack::CONTENT_TYPE]).to eq('application/x-ruby')
         expect(last_response.headers['Content-Disposition']).to eq("attachment; filename*=UTF-8''api_spec.rb")
         File.open(filename, 'rb') do |io|
           expect(last_response.body).to eq io.read
diff --git a/spec/grape/dsl/inside_route_spec.rb b/spec/grape/dsl/inside_route_spec.rb
index 6dff2d15c8..551a3ca193 100644
--- a/spec/grape/dsl/inside_route_spec.rb
+++ b/spec/grape/dsl/inside_route_spec.rb
@@ -263,9 +263,9 @@ def initialize
         end
 
         before do
-          subject.header Grape::Http::Headers::CACHE_CONTROL, 'cache'
-          subject.header Grape::Http::Headers::CONTENT_LENGTH, 123
-          subject.header Grape::Http::Headers::TRANSFER_ENCODING, 'base64'
+          subject.header Rack::CACHE_CONTROL, 'cache'
+          subject.header Rack::CONTENT_LENGTH, 123
+          subject.header Rack::TRANSFER_ENCODING, 'base64'
         end
 
         it 'sends no deprecation warnings' do
@@ -283,19 +283,19 @@ def initialize
         it 'does not change the Cache-Control header' do
           subject.sendfile file_path
 
-          expect(subject.header[Grape::Http::Headers::CACHE_CONTROL]).to eq 'cache'
+          expect(subject.header[Rack::CACHE_CONTROL]).to eq 'cache'
         end
 
         it 'does not change the Content-Length header' do
           subject.sendfile file_path
 
-          expect(subject.header[Grape::Http::Headers::CONTENT_LENGTH]).to eq 123
+          expect(subject.header[Rack::CONTENT_LENGTH]).to eq 123
         end
 
         it 'does not change the Transfer-Encoding header' do
           subject.sendfile file_path
 
-          expect(subject.header[Grape::Http::Headers::TRANSFER_ENCODING]).to eq 'base64'
+          expect(subject.header[Rack::TRANSFER_ENCODING]).to eq 'base64'
         end
       end
 
@@ -324,9 +324,9 @@ def initialize
         end
 
         before do
-          subject.header Grape::Http::Headers::CACHE_CONTROL, 'cache'
-          subject.header Grape::Http::Headers::CONTENT_LENGTH, 123
-          subject.header Grape::Http::Headers::TRANSFER_ENCODING, 'base64'
+          subject.header Rack::CACHE_CONTROL, 'cache'
+          subject.header Rack::CONTENT_LENGTH, 123
+          subject.header Rack::TRANSFER_ENCODING, 'base64'
         end
 
         it 'emits no deprecation warnings' do
@@ -344,25 +344,25 @@ def initialize
         it 'sets Cache-Control header to no-cache' do
           subject.stream file_path
 
-          expect(subject.header[Grape::Http::Headers::CACHE_CONTROL]).to eq 'no-cache'
+          expect(subject.header[Rack::CACHE_CONTROL]).to eq 'no-cache'
         end
 
         it 'does not change Cache-Control header' do
           subject.stream
 
-          expect(subject.header[Grape::Http::Headers::CACHE_CONTROL]).to eq 'cache'
+          expect(subject.header[Rack::CACHE_CONTROL]).to eq 'cache'
         end
 
         it 'sets Content-Length header to nil' do
           subject.stream file_path
 
-          expect(subject.header[Grape::Http::Headers::CONTENT_LENGTH]).to be_nil
+          expect(subject.header[Rack::CONTENT_LENGTH]).to be_nil
         end
 
         it 'sets Transfer-Encoding header to nil' do
           subject.stream file_path
 
-          expect(subject.header[Grape::Http::Headers::TRANSFER_ENCODING]).to be_nil
+          expect(subject.header[Rack::TRANSFER_ENCODING]).to be_nil
         end
       end
 
@@ -374,9 +374,9 @@ def initialize
         end
 
         before do
-          subject.header Grape::Http::Headers::CACHE_CONTROL, 'cache'
-          subject.header Grape::Http::Headers::CONTENT_LENGTH, 123
-          subject.header Grape::Http::Headers::TRANSFER_ENCODING, 'base64'
+          subject.header Rack::CACHE_CONTROL, 'cache'
+          subject.header Rack::CONTENT_LENGTH, 123
+          subject.header Rack::TRANSFER_ENCODING, 'base64'
         end
 
         it 'emits no deprecation warnings' do
@@ -394,19 +394,19 @@ def initialize
         it 'sets Cache-Control header to no-cache' do
           subject.stream stream_object
 
-          expect(subject.header[Grape::Http::Headers::CACHE_CONTROL]).to eq 'no-cache'
+          expect(subject.header[Rack::CACHE_CONTROL]).to eq 'no-cache'
         end
 
         it 'sets Content-Length header to nil' do
           subject.stream stream_object
 
-          expect(subject.header[Grape::Http::Headers::CONTENT_LENGTH]).to be_nil
+          expect(subject.header[Rack::CONTENT_LENGTH]).to be_nil
         end
 
         it 'sets Transfer-Encoding header to nil' do
           subject.stream stream_object
 
-          expect(subject.header[Grape::Http::Headers::TRANSFER_ENCODING]).to be_nil
+          expect(subject.header[Rack::TRANSFER_ENCODING]).to be_nil
         end
       end
 
@@ -421,7 +421,7 @@ def initialize
 
     it 'returns default' do
       expect(subject.stream).to be_nil
-      expect(subject.header[Grape::Http::Headers::CACHE_CONTROL]).to be_nil
+      expect(subject.header[Rack::CACHE_CONTROL]).to be_nil
     end
   end
 
diff --git a/spec/grape/endpoint_spec.rb b/spec/grape/endpoint_spec.rb
index b83c25dda6..400b45c404 100644
--- a/spec/grape/endpoint_spec.rb
+++ b/spec/grape/endpoint_spec.rb
@@ -499,7 +499,7 @@ def app
       end
 
       it 'responses with given content type in headers' do
-        expect(last_response.headers[Grape::Http::Headers::CONTENT_TYPE]).to eq 'application/json; charset=utf-8'
+        expect(last_response.headers[Rack::CONTENT_TYPE]).to eq 'application/json; charset=utf-8'
       end
     end