diff --git a/changelog/fix_a_false_negative_for_rails_action_controller_test_case.md b/changelog/fix_a_false_negative_for_rails_action_controller_test_case.md
new file mode 100644
index 0000000000..546326fb02
--- /dev/null
+++ b/changelog/fix_a_false_negative_for_rails_action_controller_test_case.md
@@ -0,0 +1 @@
+* [#824](https://github.com/rubocop/rubocop-rails/pull/824): Fix a false negative for `Rails/ActionControllerTestCase` when the class is namespaced. ([@vlad-pisanov][])
diff --git a/lib/rubocop/cop/rails/action_controller_test_case.rb b/lib/rubocop/cop/rails/action_controller_test_case.rb
index 92959c771c..a78d1d12f4 100644
--- a/lib/rubocop/cop/rails/action_controller_test_case.rb
+++ b/lib/rubocop/cop/rails/action_controller_test_case.rb
@@ -30,7 +30,7 @@ class ActionControllerTestCase < Base
 
         def_node_matcher :action_controller_test_case?, <<~PATTERN
           (class
-            (const nil? _)
+            (const _ _)
             (const (const {nil? cbase} :ActionController) :TestCase) _)
         PATTERN
 
diff --git a/spec/rubocop/cop/rails/action_controller_test_case_spec.rb b/spec/rubocop/cop/rails/action_controller_test_case_spec.rb
index a9ac35989d..0ad152c3e8 100644
--- a/spec/rubocop/cop/rails/action_controller_test_case_spec.rb
+++ b/spec/rubocop/cop/rails/action_controller_test_case_spec.rb
@@ -53,6 +53,19 @@ def test_foo
     RUBY
   end
 
+  it 'adds offense when extending `ActionController::TestCase` with a namespace' do
+    expect_offense(<<~RUBY)
+      class Foo::Bar::MyControllerTest < ActionController::TestCase
+                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `ActionDispatch::IntegrationTest` instead.
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      class Foo::Bar::MyControllerTest < ActionDispatch::IntegrationTest
+      end
+    RUBY
+  end
+
   it 'does not add offense when extending `ActionDispatch::IntegrationTest`' do
     expect_no_offenses(<<~RUBY)
       class MyControllerTest < ActionDispatch::IntegrationTest