* variant.
  */
 #define FIXTURE_VARIANT_ADD(fixture_name, variant_name) \
-       extern FIXTURE_VARIANT(fixture_name) \
+       extern const FIXTURE_VARIANT(fixture_name) \
                _##fixture_name##_##variant_name##_variant; \
        static struct __fixture_variant_metadata \
                _##fixture_name##_##variant_name##_object = \
                __register_fixture_variant(&_##fixture_name##_fixture_object, \
                        &_##fixture_name##_##variant_name##_object);    \
        } \
-       FIXTURE_VARIANT(fixture_name) \
+       const FIXTURE_VARIANT(fixture_name) \
                _##fixture_name##_##variant_name##_variant =
 
 /**