diff --git a/test/test_grammars.rb b/test/test_grammars.rb
index 871ba195..0ea12081 100644
--- a/test/test_grammars.rb
+++ b/test/test_grammars.rb
@@ -39,7 +39,7 @@ class TestGrammars < Minitest::Test
 
   def test_local_scopes_are_in_sync
     actual = YAML.load(`"#{File.join(ROOT, "script", "convert-grammars")}" --output - --no-install --no-remote 2>/dev/null`)
-    assert_predicate $?, :success?
+    assert $?.success?, "script/convert-grammars failed"
 
     # We're not checking remote grammars. That can take a long time and make CI
     # flaky if network conditions are poor.