diff --git a/test/material_async_button_theme_test.dart b/test/material_async_button_theme_test.dart
index 036b383..5f2b08a 100644
--- a/test/material_async_button_theme_test.dart
+++ b/test/material_async_button_theme_test.dart
@@ -114,5 +114,16 @@ void main() {
       check(a).equals(b);
       check(a.hashCode).equals(b.hashCode);
     });
+
+    test('empty leaves every field at its default', () {
+      // `empty` is itself `const AsyncButtonTheme()`, so the equality below is
+      // satisfied by const canonicalization alone. The field checks are what
+      // actually pin the invariant: `empty` must never grow a set field.
+      // ignore: use_named_constants
+      const b = AsyncButtonTheme();
+      check(AsyncButtonTheme.empty).equals(b);
+      check(AsyncButtonTheme.empty.loadingBuilder).isNull();
+      check(AsyncButtonTheme.empty.transitionBuilder).isNull();
+    });
   });
 }