diff --git a/app/controllers/projects/blob_controller.rb b/app/controllers/projects/blob_controller.rb
index 39ba815cfca..f9a5ef46786 100644
--- a/app/controllers/projects/blob_controller.rb
+++ b/app/controllers/projects/blob_controller.rb
@@ -5,7 +5,7 @@ class Projects::BlobController < Projects::ApplicationController
   include ActionView::Helpers::SanitizeHelper
 
   # Raised when given an invalid file path
-  class InvalidPathError < StandardError; end
+  InvalidPathError = Class.new(StandardError)
 
   before_action :require_non_empty_project, except: [:new, :create]
   before_action :authorize_download_code!
diff --git a/app/models/project.rb b/app/models/project.rb
index e06fc30dc8a..0c2494d3c32 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -19,7 +19,7 @@ class Project < ActiveRecord::Base
 
   extend Gitlab::ConfigHelper
 
-  class BoardLimitExceeded < StandardError; end
+  BoardLimitExceeded = Class.new(StandardError)
 
   NUMBER_OF_PERMITTED_BOARDS = 1
   UNKNOWN_IMPORT_URL = 'http://unknown.git'.freeze
diff --git a/app/models/project_wiki.rb b/app/models/project_wiki.rb
index 9891f5edf41..539b31780b3 100644
--- a/app/models/project_wiki.rb
+++ b/app/models/project_wiki.rb
@@ -7,7 +7,7 @@ class ProjectWiki
     'AsciiDoc' => :asciidoc
   }.freeze unless defined?(MARKUPS)
 
-  class CouldNotCreateWikiError < StandardError; end
+  CouldNotCreateWikiError = Class.new(StandardError)
 
   # Returns a string describing what went wrong after
   # an operation fails.
diff --git a/app/serializers/pipeline_serializer.rb b/app/serializers/pipeline_serializer.rb
index 2bc6cf3266e..ab2d3d5a3ec 100644
--- a/app/serializers/pipeline_serializer.rb
+++ b/app/serializers/pipeline_serializer.rb
@@ -1,5 +1,5 @@
 class PipelineSerializer < BaseSerializer
-  class InvalidResourceError < StandardError; end
+  InvalidResourceError = Class.new(StandardError)
 
   entity PipelineEntity
 
diff --git a/app/services/commits/change_service.rb b/app/services/commits/change_service.rb
index 25e22f14e60..8a9bcd2d053 100644
--- a/app/services/commits/change_service.rb
+++ b/app/services/commits/change_service.rb
@@ -1,7 +1,7 @@
 module Commits
   class ChangeService < ::BaseService
-    class ValidationError < StandardError; end
-    class ChangeError < StandardError; end
+    ValidationError = Class.new(StandardError)
+    ChangeError = Class.new(StandardError)
 
     def execute
       @start_project = params[:start_project] || @project
diff --git a/app/services/files/base_service.rb b/app/services/files/base_service.rb
index 0a25f56d24c..31869c2f01e 100644
--- a/app/services/files/base_service.rb
+++ b/app/services/files/base_service.rb
@@ -1,6 +1,6 @@
 module Files
   class BaseService < ::BaseService
-    class ValidationError < StandardError; end
+    ValidationError = Class.new(StandardError)
 
     def execute
       @start_project = params[:start_project] || @project
diff --git a/app/services/files/multi_service.rb b/app/services/files/multi_service.rb
index 0609c6219e7..700f9f4f6f0 100644
--- a/app/services/files/multi_service.rb
+++ b/app/services/files/multi_service.rb
@@ -1,6 +1,6 @@
 module Files
   class MultiService < Files::BaseService
-    class FileChangedError < StandardError; end
+    FileChangedError = Class.new(StandardError)
 
     ACTIONS = %w[create update delete move].freeze
 
diff --git a/app/services/files/update_service.rb b/app/services/files/update_service.rb
index 54e1aaf3f67..fbbab97632e 100644
--- a/app/services/files/update_service.rb
+++ b/app/services/files/update_service.rb
@@ -1,6 +1,6 @@
 module Files
   class UpdateService < Files::BaseService
-    class FileChangedError < StandardError; end
+    FileChangedError = Class.new(StandardError)
 
     def commit
       repository.update_file(current_user, @file_path, @file_content,
diff --git a/app/services/issues/move_service.rb b/app/services/issues/move_service.rb
index a2a5f57d069..711f4035c55 100644
--- a/app/services/issues/move_service.rb
+++ b/app/services/issues/move_service.rb
@@ -1,6 +1,6 @@
 module Issues
   class MoveService < Issues::BaseService
-    class MoveError < StandardError; end
+    MoveError = Class.new(StandardError)
 
     def execute(issue, new_project)
       @old_issue = issue
diff --git a/app/services/merge_requests/resolve_service.rb b/app/services/merge_requests/resolve_service.rb
index d22a1d3e0ad..82cd89d9a0b 100644
--- a/app/services/merge_requests/resolve_service.rb
+++ b/app/services/merge_requests/resolve_service.rb
@@ -1,7 +1,6 @@
 module MergeRequests
   class ResolveService < MergeRequests::BaseService
-    class MissingFiles < Gitlab::Conflict::ResolutionError
-    end
+    MissingFiles = Class.new(Gitlab::Conflict::ResolutionError)
 
     attr_accessor :conflicts, :rugged, :merge_index, :merge_request
 
diff --git a/app/services/projects/destroy_service.rb b/app/services/projects/destroy_service.rb
index 2e06826c311..a7142d5950e 100644
--- a/app/services/projects/destroy_service.rb
+++ b/app/services/projects/destroy_service.rb
@@ -2,7 +2,7 @@ module Projects
   class DestroyService < BaseService
     include Gitlab::ShellAdapter
 
-    class DestroyError < StandardError; end
+    DestroyError = Class.new(StandardError)
 
     DELETED_FLAG = '+deleted'.freeze
 
diff --git a/app/services/projects/import_service.rb b/app/services/projects/import_service.rb
index cd230528743..1c5a549feb9 100644
--- a/app/services/projects/import_service.rb
+++ b/app/services/projects/import_service.rb
@@ -2,7 +2,7 @@ module Projects
   class ImportService < BaseService
     include Gitlab::ShellAdapter
 
-    class Error < StandardError; end
+    Error = Class.new(StandardError)
 
     def execute
       add_repository_to_project unless project.gitlab_project_import?
diff --git a/app/services/projects/transfer_service.rb b/app/services/projects/transfer_service.rb
index 20dfbddc823..da6e6acd4a7 100644
--- a/app/services/projects/transfer_service.rb
+++ b/app/services/projects/transfer_service.rb
@@ -9,7 +9,7 @@
 module Projects
   class TransferService < BaseService
     include Gitlab::ShellAdapter
-    class TransferError < StandardError; end
+    TransferError = Class.new(StandardError)
 
     def execute(new_namespace)
       if allowed_transfer?(current_user, project, new_namespace)
diff --git a/lib/api/api_guard.rb b/lib/api/api_guard.rb
index c11f8529183..409cb5b924f 100644
--- a/lib/api/api_guard.rb
+++ b/lib/api/api_guard.rb
@@ -160,13 +160,10 @@ module API
     # Exceptions
     #
 
-    class MissingTokenError < StandardError; end
-
-    class TokenNotFoundError < StandardError; end
-
-    class ExpiredError < StandardError; end
-
-    class RevokedError < StandardError; end
+    MissingTokenError = Class.new(StandardError)
+    TokenNotFoundError = Class.new(StandardError)
+    ExpiredError = Class.new(StandardError)
+    RevokedError = Class.new(StandardError)
 
     class InsufficientScopeError < StandardError
       attr_reader :scopes
diff --git a/lib/bitbucket/error/unauthorized.rb b/lib/bitbucket/error/unauthorized.rb
index 5e2eb57bb0e..efe10542f19 100644
--- a/lib/bitbucket/error/unauthorized.rb
+++ b/lib/bitbucket/error/unauthorized.rb
@@ -1,6 +1,5 @@
 module Bitbucket
   module Error
-    class Unauthorized < StandardError
-    end
+    Unauthorized = Class.new(StandardError)
   end
 end
diff --git a/lib/ci/gitlab_ci_yaml_processor.rb b/lib/ci/gitlab_ci_yaml_processor.rb
index 649ee4d018b..e390919ae1d 100644
--- a/lib/ci/gitlab_ci_yaml_processor.rb
+++ b/lib/ci/gitlab_ci_yaml_processor.rb
@@ -1,6 +1,6 @@
 module Ci
   class GitlabCiYamlProcessor
-    class ValidationError < StandardError; end
+    ValidationError = Class.new(StandardError)
 
     include Gitlab::Ci::Config::Entry::LegacyValidationHelpers
 
diff --git a/lib/extracts_path.rb b/lib/extracts_path.rb
index 9ece84cc469..dd864eea3fa 100644
--- a/lib/extracts_path.rb
+++ b/lib/extracts_path.rb
@@ -2,7 +2,7 @@
 # file path string when combined in a request parameter
 module ExtractsPath
   # Raised when given an invalid file path
-  class InvalidPathError < StandardError; end
+  InvalidPathError = Class.new(StandardError)
 
   # Given a string containing both a Git tree-ish, such as a branch or tag, and
   # a filesystem path joined by forward slashes, attempts to separate the two.
diff --git a/lib/gitlab/access.rb b/lib/gitlab/access.rb
index 3b210eeda9d..8c28009b9c6 100644
--- a/lib/gitlab/access.rb
+++ b/lib/gitlab/access.rb
@@ -5,7 +5,7 @@
 #
 module Gitlab
   module Access
-    class AccessDeniedError < StandardError; end
+    AccessDeniedError = Class.new(StandardError)
 
     NO_ACCESS = 0
     GUEST     = 10
diff --git a/lib/gitlab/auth.rb b/lib/gitlab/auth.rb
index 89db6c3da46..0a5abc92190 100644
--- a/lib/gitlab/auth.rb
+++ b/lib/gitlab/auth.rb
@@ -1,6 +1,6 @@
 module Gitlab
   module Auth
-    class MissingPersonalTokenError < StandardError; end
+    MissingPersonalTokenError = Class.new(StandardError)
 
     SCOPES = [:api, :read_user].freeze
     DEFAULT_SCOPES = [:api].freeze
diff --git a/lib/gitlab/ci/build/artifacts/metadata.rb b/lib/gitlab/ci/build/artifacts/metadata.rb
index cd2e83b4c27..a375ccbece0 100644
--- a/lib/gitlab/ci/build/artifacts/metadata.rb
+++ b/lib/gitlab/ci/build/artifacts/metadata.rb
@@ -6,7 +6,7 @@ module Gitlab
     module Build
       module Artifacts
         class Metadata
-          class ParserError < StandardError; end
+          ParserError = Class.new(StandardError)
 
           VERSION_PATTERN = /^[\w\s]+(\d+\.\d+\.\d+)/
           INVALID_PATH_PATTERN = %r{(^\.?\.?/)|(/\.?\.?/)}
diff --git a/lib/gitlab/ci/config/entry/factory.rb b/lib/gitlab/ci/config/entry/factory.rb
index 9f5e393d191..6be8288748f 100644
--- a/lib/gitlab/ci/config/entry/factory.rb
+++ b/lib/gitlab/ci/config/entry/factory.rb
@@ -6,7 +6,7 @@ module Gitlab
         # Factory class responsible for fabricating entry objects.
         #
         class Factory
-          class InvalidFactory < StandardError; end
+          InvalidFactory = Class.new(StandardError)
 
           def initialize(entry)
             @entry = entry
diff --git a/lib/gitlab/ci/config/entry/node.rb b/lib/gitlab/ci/config/entry/node.rb
index 5eef2868cd6..55a5447ab51 100644
--- a/lib/gitlab/ci/config/entry/node.rb
+++ b/lib/gitlab/ci/config/entry/node.rb
@@ -6,7 +6,7 @@ module Gitlab
         # Base abstract class for each configuration entry node.
         #
         class Node
-          class InvalidError < StandardError; end
+          InvalidError = Class.new(StandardError)
 
           attr_reader :config, :metadata
           attr_accessor :key, :parent, :description
diff --git a/lib/gitlab/ci/config/loader.rb b/lib/gitlab/ci/config/loader.rb
index dbf6eb0edbe..e7d9f6a7761 100644
--- a/lib/gitlab/ci/config/loader.rb
+++ b/lib/gitlab/ci/config/loader.rb
@@ -2,7 +2,7 @@ module Gitlab
   module Ci
     class Config
       class Loader
-        class FormatError < StandardError; end
+        FormatError = Class.new(StandardError)
 
         def initialize(config)
           @config = YAML.safe_load(config, [Symbol], [], true)
diff --git a/lib/gitlab/conflict/file.rb b/lib/gitlab/conflict/file.rb
index d80bc748209..75a213ef752 100644
--- a/lib/gitlab/conflict/file.rb
+++ b/lib/gitlab/conflict/file.rb
@@ -4,8 +4,7 @@ module Gitlab
       include Gitlab::Routing.url_helpers
       include IconsHelper
 
-      class MissingResolution < ResolutionError
-      end
+      MissingResolution = Class.new(ResolutionError)
 
       CONTEXT_LINES = 3
 
diff --git a/lib/gitlab/conflict/file_collection.rb b/lib/gitlab/conflict/file_collection.rb
index fa5bd4649d4..990b719ecfd 100644
--- a/lib/gitlab/conflict/file_collection.rb
+++ b/lib/gitlab/conflict/file_collection.rb
@@ -1,8 +1,7 @@
 module Gitlab
   module Conflict
     class FileCollection
-      class ConflictSideMissing < StandardError
-      end
+      ConflictSideMissing = Class.new(StandardError)
 
       attr_reader :merge_request, :our_commit, :their_commit
 
diff --git a/lib/gitlab/conflict/parser.rb b/lib/gitlab/conflict/parser.rb
index ddd657903fb..d3524c338ee 100644
--- a/lib/gitlab/conflict/parser.rb
+++ b/lib/gitlab/conflict/parser.rb
@@ -1,25 +1,15 @@
 module Gitlab
   module Conflict
     class Parser
-      class UnresolvableError < StandardError
-      end
-
-      class UnmergeableFile < UnresolvableError
-      end
-
-      class UnsupportedEncoding < UnresolvableError
-      end
+      UnresolvableError = Class.new(StandardError)
+      UnmergeableFile = Class.new(UnresolvableError)
+      UnsupportedEncoding = Class.new(UnresolvableError)
 
       # Recoverable errors - the conflict can be resolved in an editor, but not with
       # sections.
-      class ParserError < StandardError
-      end
-
-      class UnexpectedDelimiter < ParserError
-      end
-
-      class MissingEndDelimiter < ParserError
-      end
+      ParserError = Class.new(StandardError)
+      UnexpectedDelimiter = Class.new(ParserError)
+      MissingEndDelimiter = Class.new(ParserError)
 
       def parse(text, our_path:, their_path:, parent_file: nil)
         raise UnmergeableFile if text.blank? # Typically a binary file
diff --git a/lib/gitlab/conflict/resolution_error.rb b/lib/gitlab/conflict/resolution_error.rb
index a0f2006bc24..0b61256b35a 100644
--- a/lib/gitlab/conflict/resolution_error.rb
+++ b/lib/gitlab/conflict/resolution_error.rb
@@ -1,6 +1,5 @@
 module Gitlab
   module Conflict
-    class ResolutionError < StandardError
-    end
+    ResolutionError = Class.new(StandardError)
   end
 end
diff --git a/lib/gitlab/email/receiver.rb b/lib/gitlab/email/receiver.rb
index b64db5d01ae..ec0529b5a4b 100644
--- a/lib/gitlab/email/receiver.rb
+++ b/lib/gitlab/email/receiver.rb
@@ -4,19 +4,19 @@ require_dependency 'gitlab/email/handler'
 # Inspired in great part by Discourse's Email::Receiver
 module Gitlab
   module Email
-    class ProcessingError < StandardError; end
-    class EmailUnparsableError < ProcessingError; end
-    class SentNotificationNotFoundError < ProcessingError; end
-    class ProjectNotFound < ProcessingError; end
-    class EmptyEmailError < ProcessingError; end
-    class AutoGeneratedEmailError < ProcessingError; end
-    class UserNotFoundError < ProcessingError; end
-    class UserBlockedError < ProcessingError; end
-    class UserNotAuthorizedError < ProcessingError; end
-    class NoteableNotFoundError < ProcessingError; end
-    class InvalidNoteError < ProcessingError; end
-    class InvalidIssueError < ProcessingError; end
-    class UnknownIncomingEmail < ProcessingError; end
+    ProcessingError = Class.new(StandardError)
+    EmailUnparsableError = Class.new(ProcessingError)
+    SentNotificationNotFoundError = Class.new(ProcessingError)
+    ProjectNotFound = Class.new(ProcessingError)
+    EmptyEmailError = Class.new(ProcessingError)
+    AutoGeneratedEmailError = Class.new(ProcessingError)
+    UserNotFoundError = Class.new(ProcessingError)
+    UserBlockedError = Class.new(ProcessingError)
+    UserNotAuthorizedError = Class.new(ProcessingError)
+    NoteableNotFoundError = Class.new(ProcessingError)
+    InvalidNoteError = Class.new(ProcessingError)
+    InvalidIssueError = Class.new(ProcessingError)
+    UnknownIncomingEmail = Class.new(ProcessingError)
 
     class Receiver
       def initialize(raw)
diff --git a/lib/gitlab/git/diff.rb b/lib/gitlab/git/diff.rb
index d6b3b5705a9..2a017c93f57 100644
--- a/lib/gitlab/git/diff.rb
+++ b/lib/gitlab/git/diff.rb
@@ -2,7 +2,7 @@
 module Gitlab
   module Git
     class Diff
-      class TimeoutError < StandardError; end
+      TimeoutError = Class.new(StandardError)
       include Gitlab::Git::EncodingHelper
 
       # Diff properties
diff --git a/lib/gitlab/git/repository.rb b/lib/gitlab/git/repository.rb
index 8ec90885231..0e9b812ffdd 100644
--- a/lib/gitlab/git/repository.rb
+++ b/lib/gitlab/git/repository.rb
@@ -10,9 +10,9 @@ module Gitlab
 
       SEARCH_CONTEXT_LINES = 3
 
-      class NoRepository < StandardError; end
-      class InvalidBlobName < StandardError; end
-      class InvalidRef < StandardError; end
+      NoRepository = Class.new(StandardError)
+      InvalidBlobName = Class.new(StandardError)
+      InvalidRef = Class.new(StandardError)
 
       # Full path to repo
       attr_reader :path
diff --git a/lib/gitlab/import_export/error.rb b/lib/gitlab/import_export/error.rb
index e341c4d9cf8..788eedf2686 100644
--- a/lib/gitlab/import_export/error.rb
+++ b/lib/gitlab/import_export/error.rb
@@ -1,5 +1,5 @@
 module Gitlab
   module ImportExport
-    class Error < StandardError; end
+    Error = Class.new(StandardError)
   end
 end
diff --git a/lib/gitlab/o_auth/user.rb b/lib/gitlab/o_auth/user.rb
index 95d2f559588..fcf51b7fc5b 100644
--- a/lib/gitlab/o_auth/user.rb
+++ b/lib/gitlab/o_auth/user.rb
@@ -5,7 +5,7 @@
 #
 module Gitlab
   module OAuth
-    class SignupDisabledError < StandardError; end
+    SignupDisabledError = Class.new(StandardError)
 
     class User
       attr_accessor :auth_hash, :gl_user
diff --git a/lib/gitlab/route_map.rb b/lib/gitlab/route_map.rb
index 72d00abfcc2..36791fae60f 100644
--- a/lib/gitlab/route_map.rb
+++ b/lib/gitlab/route_map.rb
@@ -1,6 +1,6 @@
 module Gitlab
   class RouteMap
-    class FormatError < StandardError; end
+    FormatError = Class.new(StandardError)
 
     def initialize(data)
       begin
diff --git a/lib/gitlab/serializer/pagination.rb b/lib/gitlab/serializer/pagination.rb
index bf2c0acc729..9c92b83dddc 100644
--- a/lib/gitlab/serializer/pagination.rb
+++ b/lib/gitlab/serializer/pagination.rb
@@ -1,7 +1,7 @@
 module Gitlab
   module Serializer
     class Pagination
-      class InvalidResourceError < StandardError; end
+      InvalidResourceError = Class.new(StandardError)
       include ::API::Helpers::Pagination
 
       def initialize(request, response)
diff --git a/lib/gitlab/shell.rb b/lib/gitlab/shell.rb
index 7374d2bc8b8..da8d8ddb8ed 100644
--- a/lib/gitlab/shell.rb
+++ b/lib/gitlab/shell.rb
@@ -2,7 +2,7 @@ require 'securerandom'
 
 module Gitlab
   class Shell
-    class Error < StandardError; end
+    Error = Class.new(StandardError)
 
     KeyAdder = Struct.new(:io) do
       def add_key(id, key)
diff --git a/lib/gitlab/template/finders/repo_template_finder.rb b/lib/gitlab/template/finders/repo_template_finder.rb
index 22c39436cb2..cb7957e2af9 100644
--- a/lib/gitlab/template/finders/repo_template_finder.rb
+++ b/lib/gitlab/template/finders/repo_template_finder.rb
@@ -4,7 +4,7 @@ module Gitlab
     module Finders
       class RepoTemplateFinder < BaseTemplateFinder
         # Raised when file is not found
-        class FileNotFoundError < StandardError; end
+        FileNotFoundError = Class.new(StandardError)
 
         def initialize(project, base_dir, extension, categories = {})
           @categories     = categories
diff --git a/lib/gitlab/update_path_error.rb b/lib/gitlab/update_path_error.rb
index ce14cc887d0..8947ecfb92e 100644
--- a/lib/gitlab/update_path_error.rb
+++ b/lib/gitlab/update_path_error.rb
@@ -1,3 +1,3 @@
 module Gitlab
-  class UpdatePathError < StandardError; end
+  UpdatePathError = Class.new(StandardError)
 end
diff --git a/lib/mattermost/client.rb b/lib/mattermost/client.rb
index e55c0d6ac49..ad6df246091 100644
--- a/lib/mattermost/client.rb
+++ b/lib/mattermost/client.rb
@@ -1,5 +1,5 @@
 module Mattermost
-  class ClientError < Mattermost::Error; end
+  ClientError = Class.new(Mattermost::Error)
 
   class Client
     attr_reader :user
diff --git a/lib/mattermost/error.rb b/lib/mattermost/error.rb
index 014df175be0..dee6deb7974 100644
--- a/lib/mattermost/error.rb
+++ b/lib/mattermost/error.rb
@@ -1,3 +1,3 @@
 module Mattermost
-  class Error < StandardError; end
+  Error = Class.new(StandardError)
 end
diff --git a/lib/mattermost/session.rb b/lib/mattermost/session.rb
index 377cb7b1021..5388966605d 100644
--- a/lib/mattermost/session.rb
+++ b/lib/mattermost/session.rb
@@ -5,7 +5,7 @@ module Mattermost
     end
   end
 
-  class ConnectionError < Mattermost::Error; end
+  ConnectionError = Class.new(Mattermost::Error)
 
   # This class' prime objective is to obtain a session token on a Mattermost
   # instance with SSO configured where this GitLab instance is the provider.
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index d4266d0deae..ea8e0f64b0d 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -1,3 +1,4 @@
+require_relative 'cop/custom_error_class'
 require_relative 'cop/gem_fetcher'
 require_relative 'cop/migration/add_column'
 require_relative 'cop/migration/add_column_with_default'