diff --git a/actionpack/lib/action_dispatch/http/request.rb b/actionpack/lib/action_dispatch/http/request.rb
index 2da485884a871..e7b930eed797c 100644
--- a/actionpack/lib/action_dispatch/http/request.rb
+++ b/actionpack/lib/action_dispatch/http/request.rb
@@ -290,6 +290,7 @@ def media_type
 
     # Returns the content length of the request as an integer.
     def content_length
+      return raw_post.bytesize if headers.key?("Transfer-Encoding")
       super.to_i
     end
 
@@ -344,9 +345,8 @@ def server_software
     # work with raw requests directly.
     def raw_post
       unless has_header? "RAW_POST_DATA"
-        raw_post_body = body
-        set_header("RAW_POST_DATA", raw_post_body.read(content_length))
-        raw_post_body.rewind if raw_post_body.respond_to?(:rewind)
+        set_header("RAW_POST_DATA", read_body_stream)
+        body_stream.rewind if body_stream.respond_to?(:rewind)
       end
       get_header "RAW_POST_DATA"
     end
@@ -472,6 +472,12 @@ def check_method(name)
       def default_session
         Session.disabled(self)
       end
+
+      def read_body_stream
+        body_stream.rewind if body_stream.respond_to?(:rewind)
+        return body_stream.read if headers.key?("Transfer-Encoding") # Read body stream until EOF if "Transfer-Encoding" is present
+        body_stream.read(content_length)
+      end
   end
 end
 
diff --git a/railties/test/railties/http_request_test.rb b/railties/test/railties/http_request_test.rb
new file mode 100644
index 0000000000000..ece2bc481a9d3
--- /dev/null
+++ b/railties/test/railties/http_request_test.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require "isolation/abstract_unit"
+require "stringio"
+require "rack/test"
+require "active_support/core_ext/module/delegation"
+
+module RailtiesTest
+  class HttpRequestTest < ActiveSupport::TestCase
+    include ActiveSupport::Testing::Isolation
+    include Rack::Test::Methods
+
+    def setup
+      build_app
+
+      app_file "config/routes.rb", <<-RUBY
+        Rails.application.routes.draw do
+          post "posts", to: "posts#create"
+        end
+      RUBY
+
+      controller "posts", <<-RUBY
+        class PostsController < ApplicationController
+          def create
+            render json: {
+              raw_post: request.raw_post,
+              content_length: request.content_length
+            }
+          end
+        end
+      RUBY
+    end
+
+    def teardown
+      teardown_app
+    end
+
+    class TestInput < StringIO
+      undef_method :size
+    end
+
+    test "parses request raw_post correctly when request has Transfer-Encoding header without a Content-Length value" do
+      require "#{app_path}/config/environment"
+
+      header "Transfer-Encoding", "gzip, chunked;foo=bar"
+      post "/posts", TestInput.new("foo=bar") # prevents Rack::MockRequest from adding a Content-Length
+
+      json_response = JSON.parse(last_response.body)
+      assert_equal 7, json_response["content_length"]
+      assert_equal "foo=bar", json_response["raw_post"]
+    end
+  end
+end