diff --git a/lib/httpi.rb b/lib/httpi.rb
index 61613c2..f4c377b 100644
--- a/lib/httpi.rb
+++ b/lib/httpi.rb
@@ -3,6 +3,7 @@
 require "httpi/logger"
 require "httpi/request"
 require "httpi/query_builder"
+require "httpi/utils"
 
 require "httpi/adapter/httpclient"
 require "httpi/adapter/curb"
diff --git a/lib/httpi/request.rb b/lib/httpi/request.rb
index 786e14c..b646795 100644
--- a/lib/httpi/request.rb
+++ b/lib/httpi/request.rb
@@ -64,12 +64,12 @@ def ssl?
 
     # Returns a Hash of HTTP headers. Defaults to return an empty Hash.
     def headers
-      @headers ||= Rack::Headers.new
+      @headers ||= HTTPI::Utils::Headers.new
     end
 
     # Sets the Hash of HTTP headers.
     def headers=(headers)
-      @headers = Rack::Headers.new.merge(headers)
+      @headers = HTTPI::Utils::Headers.new.merge(headers)
     end
 
     # Adds a header information to accept gzipped content.
diff --git a/lib/httpi/response.rb b/lib/httpi/response.rb
index f9b7c4f..ecc3d41 100644
--- a/lib/httpi/response.rb
+++ b/lib/httpi/response.rb
@@ -20,7 +20,7 @@ class Response
     # Initializer expects an HTTP response +code+, +headers+ and +body+.
     def initialize(code, headers, body)
       self.code = code.to_i
-      self.headers = Rack::Headers.new.merge(headers)
+      self.headers = HTTPI::Utils::Headers.new.merge(headers)
       self.raw_body = body
     end
 
diff --git a/lib/httpi/utils.rb b/lib/httpi/utils.rb
new file mode 100644
index 0000000..ddc16e6
--- /dev/null
+++ b/lib/httpi/utils.rb
@@ -0,0 +1,238 @@
+# mostly verbatim from: https://github.com/rack/rack/blob/main/lib/rack/headers.rb
+# Because this is part of httpi's public API, its better not to load an external 
+# library for it. 
+module HTTPI
+  module Utils
+    # HTTPI::Utils::Headers is a Hash subclass that downcases all keys.
+    class Headers < Hash
+      KNOWN_HEADERS = {}
+      %w(
+        Accept-CH
+        Accept-Patch
+        Accept-Ranges
+        Access-Control-Allow-Credentials
+        Access-Control-Allow-Headers
+        Access-Control-Allow-Methods
+        Access-Control-Allow-Origin
+        Access-Control-Expose-Headers
+        Access-Control-Max-Age
+        Age
+        Allow
+        Alt-Svc
+        Cache-Control
+        Connection
+        Content-Disposition
+        Content-Encoding
+        Content-Language
+        Content-Length
+        Content-Location
+        Content-MD5
+        Content-Range
+        Content-Security-Policy
+        Content-Security-Policy-Report-Only
+        Content-Type
+        Date
+        Delta-Base
+        ETag
+        Expect-CT
+        Expires
+        Feature-Policy
+        IM
+        Last-Modified
+        Link
+        Location
+        NEL
+        P3P
+        Permissions-Policy
+        Pragma
+        Preference-Applied
+        Proxy-Authenticate
+        Public-Key-Pins
+        Referrer-Policy
+        Refresh
+        Report-To
+        Retry-After
+        Server
+        Set-Cookie
+        Status
+        Strict-Transport-Security
+        Timing-Allow-Origin
+        Tk
+        Trailer
+        Transfer-Encoding
+        Upgrade
+        Vary
+        Via
+        WWW-Authenticate
+        Warning
+        X-Cascade
+        X-Content-Duration
+        X-Content-Security-Policy
+        X-Content-Type-Options
+        X-Correlation-ID
+        X-Correlation-Id
+        X-Download-Options
+        X-Frame-Options
+        X-Permitted-Cross-Domain-Policies
+        X-Powered-By
+        X-Redirect-By
+        X-Request-ID
+        X-Request-Id
+        X-Runtime
+        X-UA-Compatible
+        X-WebKit-CS
+        X-XSS-Protection
+      ).each do |str|
+        downcased = str.downcase.freeze
+        KNOWN_HEADERS[str] = KNOWN_HEADERS[downcased] = downcased
+      end
+
+      def self.[](*items)
+        if items.length % 2 != 0
+          if items.length == 1 && items.first.is_a?(Hash)
+            new.merge!(items.first)
+          else
+            raise ArgumentError, "odd number of arguments for Utils::Headers"
+          end
+        else
+          hash = new
+          loop do
+            break if items.length == 0
+            key = items.shift
+            value = items.shift
+            hash[key] = value
+          end
+          hash
+        end
+      end
+
+      def [](key)
+        super(downcase_key(key))
+      end
+
+      def []=(key, value)
+        super(KNOWN_HEADERS[key] || key.downcase.freeze, value)
+      end
+      alias store []=
+
+      def assoc(key)
+        super(downcase_key(key))
+      end
+
+      def compare_by_identity
+        raise TypeError, "Utils::Headers cannot compare by identity, use regular Hash"
+      end
+
+      def delete(key)
+        super(downcase_key(key))
+      end
+
+      def dig(key, *a)
+        super(downcase_key(key), *a)
+      end
+
+      def fetch(key, *default, &block)
+        key = downcase_key(key)
+        super
+      end
+
+      def fetch_values(*a)
+        super(*a.map!{|key| downcase_key(key)})
+      end
+
+      def has_key?(key)
+        super(downcase_key(key))
+      end
+      alias include? has_key?
+      alias key? has_key?
+      alias member? has_key?
+
+      def invert
+        hash = self.class.new
+        each{|key, value| hash[value] = key}
+        hash
+      end
+
+      def merge(hash, &block)
+        dup.merge!(hash, &block)
+      end
+
+      def reject(&block)
+        hash = dup
+        hash.reject!(&block)
+        hash
+      end
+
+      def replace(hash)
+        clear
+        update(hash)
+      end
+
+      def select(&block)
+        hash = dup
+        hash.select!(&block)
+        hash
+      end
+
+      def to_proc
+        lambda{|x| self[x]}
+      end
+
+      def transform_values(&block)
+        dup.transform_values!(&block)
+      end
+
+      def update(hash, &block)
+        hash.each do |key, value|
+          self[key] = if block_given? && include?(key)
+            block.call(key, self[key], value)
+          else
+            value
+          end
+        end
+        self
+      end
+      alias merge! update
+
+      def values_at(*keys)
+        keys.map{|key| self[key]}
+      end
+
+      # :nocov:
+      if RUBY_VERSION >= '2.5'
+      # :nocov:
+        def slice(*a)
+          h = self.class.new
+          a.each{|k| h[k] = self[k] if has_key?(k)}
+          h
+        end
+
+        def transform_keys(&block)
+          dup.transform_keys!(&block)
+        end
+
+        def transform_keys!
+          hash = self.class.new
+          each do |k, v|
+            hash[yield k] = v
+          end
+          replace(hash)
+        end
+      end
+
+      # :nocov:
+      if RUBY_VERSION >= '3.0'
+      # :nocov:
+        def except(*a)
+          super(*a.map!{|key| downcase_key(key)})
+        end
+      end
+
+      private
+
+      def downcase_key(key)
+        key.is_a?(String) ? KNOWN_HEADERS[key] || key.downcase : key
+      end
+    end
+  end
+end
diff --git a/spec/httpi/request_spec.rb b/spec/httpi/request_spec.rb
index efd88ae..3d30528 100644
--- a/spec/httpi/request_spec.rb
+++ b/spec/httpi/request_spec.rb
@@ -149,7 +149,7 @@
   describe "#headers" do
     it "lets you specify a Hash of HTTP request headers" do
       request.headers = { "Accept-Encoding" => "gzip" }
-      expect(request.headers).to eq Rack::Headers.new.merge({ "Accept-Encoding" => "gzip" })
+      expect(request.headers).to eq HTTPI::Utils::Headers.new.merge({ "Accept-Encoding" => "gzip" })
     end
 
     it "defaults to return an empty Hash" do
diff --git a/spec/httpi/response_spec.rb b/spec/httpi/response_spec.rb
index d797bb3..699905e 100644
--- a/spec/httpi/response_spec.rb
+++ b/spec/httpi/response_spec.rb
@@ -88,7 +88,7 @@
 
     describe "#headers" do
       it "returns the HTTP response headers" do
-        expect(response.headers).to eq Rack::Headers.new.merge({ "Content-Encoding" => "gzip" })
+        expect(response.headers).to eq HTTPI::Utils::Headers.new.merge({ "Content-Encoding" => "gzip" })
       end
     end
 
@@ -116,7 +116,7 @@
 
     describe "#headers" do
       it "returns the HTTP response headers" do
-        expect(response.headers).to eq Rack::Headers.new.merge({ "Content-Type" => "application/dime" })
+        expect(response.headers).to eq HTTPI::Utils::Headers.new.merge({ "Content-Type" => "application/dime" })
       end
     end