diff --git a/changelog/fix_an_error_for_minitest_test_file_name.md b/changelog/fix_an_error_for_minitest_test_file_name.md
new file mode 100644
index 00000000..78512c29
--- /dev/null
+++ b/changelog/fix_an_error_for_minitest_test_file_name.md
@@ -0,0 +1 @@
+* [#225](https://github.com/rubocop/rubocop-minitest/issues/225): Fix an error for `Minitest/TestFileName` when using empty file. ([@koic][])
diff --git a/lib/rubocop/cop/minitest/test_file_name.rb b/lib/rubocop/cop/minitest/test_file_name.rb
index 483e7d3f..e6f6711d 100644
--- a/lib/rubocop/cop/minitest/test_file_name.rb
+++ b/lib/rubocop/cop/minitest/test_file_name.rb
@@ -21,7 +21,8 @@ class TestFileName < Base
         MSG = 'Test file path should start with `test_` or end with `_test.rb`.'
 
         def on_new_investigation
-          return unless test_file?(processed_source.ast)
+          return unless (ast = processed_source.ast)
+          return unless test_file?(ast)
 
           add_global_offense(MSG) unless valid_file_name?
         end
diff --git a/test/rubocop/cop/minitest/test_file_name_test.rb b/test/rubocop/cop/minitest/test_file_name_test.rb
index a7fa2ba7..11b7d093 100644
--- a/test/rubocop/cop/minitest/test_file_name_test.rb
+++ b/test/rubocop/cop/minitest/test_file_name_test.rb
@@ -44,4 +44,8 @@ def test_does_not_register_offense_for_non_test_classes
       class Foo; end
     RUBY
   end
+
+  def test_does_not_register_offense_for_empty_file
+    assert_no_offenses('', 'lib/foo.rb')
+  end
 end