diff --git a/.rubocop.yml b/.rubocop.yml
index 2ce32ca5002..af26abec80f 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -110,7 +110,7 @@ Style/ClassAndModuleChildren:
 
 # Enforces consistent use of `Object#is_a?` or `Object#kind_of?`.
 Style/ClassCheck:
-  Enabled: false
+  Enabled: true
 
 # Use self when defining module/class methods.
 Style/ClassMethods:
diff --git a/app/helpers/issuables_helper.rb b/app/helpers/issuables_helper.rb
index b65edb4049c..715072290c6 100644
--- a/app/helpers/issuables_helper.rb
+++ b/app/helpers/issuables_helper.rb
@@ -23,7 +23,7 @@ module IssuablesHelper
   def issuable_json_path(issuable)
     project = issuable.project
 
-    if issuable.kind_of?(MergeRequest)
+    if issuable.is_a?(MergeRequest)
       namespace_project_merge_request_path(project.namespace, project, issuable.iid, :json)
     else
       namespace_project_issue_path(project.namespace, project, issuable.iid, :json)
diff --git a/app/helpers/namespaces_helper.rb b/app/helpers/namespaces_helper.rb
index dc5ae8edbb2..2e3a15bc1b9 100644
--- a/app/helpers/namespaces_helper.rb
+++ b/app/helpers/namespaces_helper.rb
@@ -33,7 +33,7 @@ module NamespacesHelper
   end
 
   def namespace_icon(namespace, size = 40)
-    if namespace.kind_of?(Group)
+    if namespace.is_a?(Group)
       group_icon(namespace)
     else
       avatar_icon(namespace.owner.email, size)
diff --git a/app/models/ci/build.rb b/app/models/ci/build.rb
index de9fe352059..7e21eb22e27 100644
--- a/app/models/ci/build.rb
+++ b/app/models/ci/build.rb
@@ -257,7 +257,7 @@ module Ci
       return unless regex
 
       matches = text.scan(Regexp.new(regex)).last
-      matches = matches.last if matches.kind_of?(Array)
+      matches = matches.last if matches.is_a?(Array)
       coverage = matches.gsub(/\d+(\.\d+)?/).first
 
       if coverage.present?
diff --git a/app/models/commit.rb b/app/models/commit.rb
index 8f6179f183e..dc971e710ff 100644
--- a/app/models/commit.rb
+++ b/app/models/commit.rb
@@ -27,7 +27,7 @@ class Commit
   class << self
     def decorate(commits, project)
       commits.map do |commit|
-        if commit.kind_of?(Commit)
+        if commit.is_a?(Commit)
           commit
         else
           self.new(commit, project)
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index 5cb4401d69d..55b548a12f9 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -356,7 +356,7 @@ module SystemNoteService
       note:    cross_reference_note_content(gfm_reference)
     }
 
-    if noteable.kind_of?(Commit)
+    if noteable.is_a?(Commit)
       note_options.merge!(noteable_type: 'Commit', commit_id: noteable.id)
     else
       note_options[:noteable] = noteable
diff --git a/lib/file_size_validator.rb b/lib/file_size_validator.rb
index 440dd44ece7..eb19ab45ac3 100644
--- a/lib/file_size_validator.rb
+++ b/lib/file_size_validator.rb
@@ -32,9 +32,9 @@ class FileSizeValidator < ActiveModel::EachValidator
   end
 
   def validate_each(record, attribute, value)
-    raise(ArgumentError, "A CarrierWave::Uploader::Base object was expected") unless value.kind_of? CarrierWave::Uploader::Base
+    raise(ArgumentError, "A CarrierWave::Uploader::Base object was expected") unless value.is_a? CarrierWave::Uploader::Base
 
-    value = (options[:tokenizer] || DEFAULT_TOKENIZER).call(value) if value.kind_of?(String)
+    value = (options[:tokenizer] || DEFAULT_TOKENIZER).call(value) if value.is_a?(String)
 
     CHECKS.each do |key, validity_check|
       next unless check_value = options[key]
diff --git a/lib/gitlab/changes_list.rb b/lib/gitlab/changes_list.rb
index 95308aca95f..5b32fca00a4 100644
--- a/lib/gitlab/changes_list.rb
+++ b/lib/gitlab/changes_list.rb
@@ -5,7 +5,7 @@ module Gitlab
     attr_reader :raw_changes
 
     def initialize(changes)
-      @raw_changes = changes.kind_of?(String) ? changes.lines : changes
+      @raw_changes = changes.is_a?(String) ? changes.lines : changes
     end
 
     def each(&block)
diff --git a/spec/support/login_helpers.rb b/spec/support/login_helpers.rb
index dd4c7287655..9ffb00be0b8 100644
--- a/spec/support/login_helpers.rb
+++ b/spec/support/login_helpers.rb
@@ -16,7 +16,7 @@ module LoginHelpers
   #   login_as(user)
   def login_as(user_or_role)
     @user =
-      if user_or_role.kind_of?(User)
+      if user_or_role.is_a?(User)
         user_or_role
       else
         create(user_or_role)
diff --git a/spec/support/matchers/access_matchers.rb b/spec/support/matchers/access_matchers.rb
index ceddb656596..7d238850520 100644
--- a/spec/support/matchers/access_matchers.rb
+++ b/spec/support/matchers/access_matchers.rb
@@ -38,7 +38,7 @@ module AccessMatchers
   end
 
   def description_for(user, type)
-    if user.kind_of?(User)
+    if user.is_a?(User)
       # User#inspect displays too much information for RSpec's descriptions
       "be #{type} for the specified user"
     else
diff --git a/spec/support/select2_helper.rb b/spec/support/select2_helper.rb
index d30cc8ff9f2..0d526045012 100644
--- a/spec/support/select2_helper.rb
+++ b/spec/support/select2_helper.rb
@@ -12,7 +12,7 @@
 
 module Select2Helper
   def select2(value, options = {})
-    raise ArgumentError, 'options must be a Hash' unless options.kind_of?(Hash)
+    raise ArgumentError, 'options must be a Hash' unless options.is_a?(Hash)
 
     selector = options.fetch(:from)