diff --git a/Rakefile b/Rakefile
index 74c98d9..95bc97c 100644
--- a/Rakefile
+++ b/Rakefile
@@ -4,8 +4,10 @@ require 'rspec/core/rake_task'
 task :load_doorkeeper do
   `rm -rf spec/`
   `git checkout spec`
-  `git submodule init`
-  `git submodule update`
+  unless Dir.exist?('doorkeeper')
+    `git submodule init`
+    `git submodule update`
+  end
   `cp -r -n doorkeeper/spec .`
   `rm -rf spec/generators/` # we are not ActiveRecord
   `bundle exec rspec`
diff --git a/config/locales/en.yml b/config/locales/en.yml
index d8858dd..fa2d3c7 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -13,6 +13,7 @@ en:
               invalid_uri: 'must be a valid URI.'
               relative_uri: 'must be an absolute URI.'
               secured_uri: 'must be an HTTPS/SSL URI.'
+              forbidden_uri: 'is forbidden by the server.'
 
   mongoid:
     <<: *orm
diff --git a/doorkeeper b/doorkeeper
index 0e1cc96..62289ad 160000
--- a/doorkeeper
+++ b/doorkeeper
@@ -1 +1 @@
-Subproject commit 0e1cc9606b82f5fda8363d79a8955e727e761c7d
+Subproject commit 62289ad49f423cadbfbf1435ffd0046b71fc0ea3
diff --git a/doorkeeper-mongodb.gemspec b/doorkeeper-mongodb.gemspec
index 5099a77..cb5cef7 100644
--- a/doorkeeper-mongodb.gemspec
+++ b/doorkeeper-mongodb.gemspec
@@ -17,7 +17,7 @@ Gem::Specification.new do |gem|
   gem.files = Dir['lib/**/*', 'config/**/*', 'MIT-LICENSE', 'Rakefile', 'README.md']
   gem.test_files = Dir['spec/**/*']
 
-  gem.add_dependency 'doorkeeper', '>= 4.0.0'
+  gem.add_dependency 'doorkeeper', '>= 4.0.0', '< 5.0'
 
   gem.add_development_dependency 'grape'
   gem.add_development_dependency 'coveralls'
diff --git a/lib/doorkeeper-mongodb/mixins/mongo_mapper/application_mixin.rb b/lib/doorkeeper-mongodb/mixins/mongo_mapper/application_mixin.rb
index 7843f8a..3f56c68 100644
--- a/lib/doorkeeper-mongodb/mixins/mongo_mapper/application_mixin.rb
+++ b/lib/doorkeeper-mongodb/mixins/mongo_mapper/application_mixin.rb
@@ -17,6 +17,10 @@ module ApplicationMixin
           validates :redirect_uri, redirect_uri: true
 
           before_validation :generate_uid, :generate_secret, on: :create
+
+          def redirect_uri=(uris)
+            super(uris.is_a?(Array) ? uris.join("\n") : uris)
+          end
         end
 
         module ClassMethods
diff --git a/lib/doorkeeper-mongodb/mixins/mongoid/access_grant_mixin.rb b/lib/doorkeeper-mongodb/mixins/mongoid/access_grant_mixin.rb
index e0fdc65..525b158 100644
--- a/lib/doorkeeper-mongodb/mixins/mongoid/access_grant_mixin.rb
+++ b/lib/doorkeeper-mongodb/mixins/mongoid/access_grant_mixin.rb
@@ -9,6 +9,7 @@ module AccessGrantMixin
         include Doorkeeper::Models::Revocable
         include Doorkeeper::Models::Accessible
         include Doorkeeper::Models::Scopes
+        include BaseMixin
 
         included do
           belongs_to_opts = {
diff --git a/lib/doorkeeper-mongodb/mixins/mongoid/access_token_mixin.rb b/lib/doorkeeper-mongodb/mixins/mongoid/access_token_mixin.rb
index b45ce12..d281fd6 100644
--- a/lib/doorkeeper-mongodb/mixins/mongoid/access_token_mixin.rb
+++ b/lib/doorkeeper-mongodb/mixins/mongoid/access_token_mixin.rb
@@ -9,6 +9,7 @@ module AccessTokenMixin
         include Doorkeeper::Models::Revocable
         include Doorkeeper::Models::Accessible
         include Doorkeeper::Models::Scopes
+        include BaseMixin
 
         included do
           belongs_to_opts = {
diff --git a/lib/doorkeeper-mongodb/mixins/mongoid/application_mixin.rb b/lib/doorkeeper-mongodb/mixins/mongoid/application_mixin.rb
index 81c0a32..ed9eb78 100644
--- a/lib/doorkeeper-mongodb/mixins/mongoid/application_mixin.rb
+++ b/lib/doorkeeper-mongodb/mixins/mongoid/application_mixin.rb
@@ -6,6 +6,7 @@ module ApplicationMixin
 
         include Doorkeeper::OAuth::Helpers
         include Doorkeeper::Models::Scopes
+        include BaseMixin
 
         included do
           has_many_options = {
@@ -25,6 +26,10 @@ module ApplicationMixin
           validates :redirect_uri, redirect_uri: true
 
           before_validation :generate_uid, :generate_secret, on: :create
+
+          def redirect_uri=(uris)
+            super(uris.is_a?(Array) ? uris.join("\n") : uris)
+          end
         end
 
         module ClassMethods