diff --git a/extra/html-extra/Tests/Fixtures/html_classes.test b/extra/html-extra/Tests/Fixtures/html_classes.test
index d05d55f14a..1182f5ab40 100644
--- a/extra/html-extra/Tests/Fixtures/html_classes.test
+++ b/extra/html-extra/Tests/Fixtures/html_classes.test
@@ -4,14 +4,21 @@
 {{ html_classes('a', {'b': true, 'c': false}, 'd', false ? 'e', true ? 'f', '0') }}
 {% set class_a = 'a' %}
 {% set class_b = 'b' %}
-{%- set class_c -%}
-c
+{%- set class_d -%}
+d
 {%- endset -%}
 {{ html_classes(class_a, {(class_b): true})}}
-{{ html_classes(class_a, {(class_c): true})}}
+{{ html_classes(class_a, class_c, {(class_d): true})}}
 --DATA--
-return []
+return [
+    'class_c' => new class implements Stringable {
+        public function __toString(): string
+        {
+            return 'c';
+        }
+    },
+]
 --EXPECT--
 a b d f 0
 a b
-a c
+a c d