diff --git a/form/create_form_type_extension.rst b/form/create_form_type_extension.rst
index 9bb0abc2d8e..9e0066d7be8 100644
--- a/form/create_form_type_extension.rst
+++ b/form/create_form_type_extension.rst
@@ -192,7 +192,7 @@ Specifically, you need to override the ``file_widget`` block:
{% block file_widget %}
{{ block('form_widget') }}
- {% if image_url is not null %}
+ {% if image_url is defined and image_url is not null %}
{% endif %}
{% endblock %}
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