diff --git a/src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_3_layout.html.twig b/src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_3_layout.html.twig
index 99c04d8a70..0e4da9d0ee 100644
--- a/src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_3_layout.html.twig
+++ b/src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_3_layout.html.twig
@@ -160,7 +160,7 @@
         {% set label_attr = label_attr|merge({class: (label_attr.class|default('') ~ ' required')|trim}) %}
     {% endif %}
     {% if parent_label_class is defined %}
-        {% set label_attr = label_attr|merge({class: (label_attr.class|default('') ~ parent_label_class)|trim}) %}
+        {% set label_attr = label_attr|merge({class: (label_attr.class|default('') ~ ' ' ~ parent_label_class)|trim}) %}
     {% endif %}
     {% if label is empty %}
         {% set label = name|humanize %}