diff --git a/app/controllers/attachments_controller.rb b/app/controllers/attachments_controller.rb
index 1956f01e3..8e28194a3 100644
--- a/app/controllers/attachments_controller.rb
+++ b/app/controllers/attachments_controller.rb
@@ -105,7 +105,7 @@ class AttachmentsController < ApplicationController
       return
     end
 
-    @attachment = Attachment.new(:file => request.raw_post)
+    @attachment = Attachment.new(:file => request.body)
     @attachment.author = User.current
     @attachment.filename = params[:filename].presence || Redmine::Utils.random_hex(16)
     @attachment.content_type = params[:content_type].presence
diff --git a/config/initializers/10-patches.rb b/config/initializers/10-patches.rb
index cc6113d48..643d06b7e 100644
--- a/config/initializers/10-patches.rb
+++ b/config/initializers/10-patches.rb
@@ -215,3 +215,17 @@ module ActionView
     end
   end
 end
+
+# https://github.com/rack/rack/pull/1703
+# TODO: remove this when Rack is updated to 3.0.0
+require 'rack'
+module Rack
+  class RewindableInput
+    unless method_defined?(:size)
+      def size
+        make_rewindable unless @rewindable_io
+        @rewindable_io.size
+      end
+    end
+  end
+end
diff --git a/test/integration/api_test/attachments_test.rb b/test/integration/api_test/attachments_test.rb
index 545dd81f2..538649950 100644
--- a/test/integration/api_test/attachments_test.rb
+++ b/test/integration/api_test/attachments_test.rb
@@ -250,4 +250,26 @@ class Redmine::ApiTest::AttachmentsTest < Redmine::ApiTest::Base
     assert attachment.digest.present?
     assert File.exist? attachment.diskfile
   end
+
+  test "POST /uploads.json should be compatible with an fcgi's input" do
+    set_tmp_attachments_directory
+    assert_difference 'Attachment.count' do
+      post(
+        '/uploads.json',
+        :headers => {
+          "CONTENT_TYPE" => 'application/octet-stream',
+          "CONTENT_LENGTH" => '12',
+          "rack.input" => Rack::RewindableInput.new(StringIO.new('File content'))
+        }.merge(credentials('jsmith'))
+      )
+      assert_response :created
+    end
+    json = ActiveSupport::JSON.decode(response.body)
+    assert_kind_of Hash, json['upload']
+    token = json['upload']['token']
+    assert token.present?
+    assert attachment = Attachment.find_by_token(token)
+    assert_equal 12, attachment.filesize
+    assert File.exist? attachment.diskfile
+  end
 end