diff --git a/lib/classes/databox/subdefsStructure.class.php b/lib/classes/databox/subdefsStructure.class.php
index a081cf70b8..dda82dc1bf 100644
--- a/lib/classes/databox/subdefsStructure.class.php
+++ b/lib/classes/databox/subdefsStructure.class.php
@@ -179,7 +179,7 @@ class databox_subdefsStructure implements IteratorAggregate
 
     $subdef = $dom_struct->createElement('subdef');
     $subdef->setAttribute('class', $class);
-    $subdef->setAttribute('name', $name);
+    $subdef->setAttribute('name', mb_strtolower($name));
 
     $dom_xp = $this->databox->get_xpath_structure();
     $query = '//record/subdefs/subdefgroup[@name="' . $groupname . '"]';
diff --git a/lib/conf.d/data_templates/en-simple.xml b/lib/conf.d/data_templates/en-simple.xml
index 1baaa0fabb..ca1a4ada97 100644
--- a/lib/conf.d/data_templates/en-simple.xml
+++ b/lib/conf.d/data_templates/en-simple.xml
@@ -47,7 +47,7 @@
         <label lang="fr">Prévisualisation</label>
         <label lang="en">Preview</label>
       </subdef>
-      <subdef class="thumbnail" name="thumbnailGIF" downloadable="true">
+      <subdef class="thumbnail" name="thumbnailgif" downloadable="true">
         <path>{{datapathweb}}{{basename}}/subdefs</path>
         <size>200</size>
         <mediatype>gif</mediatype>
diff --git a/lib/conf.d/data_templates/fr-simple.xml b/lib/conf.d/data_templates/fr-simple.xml
index 6b7d22e9a7..757a7e8b82 100755
--- a/lib/conf.d/data_templates/fr-simple.xml
+++ b/lib/conf.d/data_templates/fr-simple.xml
@@ -45,7 +45,7 @@
         <label lang="fr">Prévisualisation</label>
         <label lang="en">Preview</label>
       </subdef>
-      <subdef class="thumbnail" name="thumbnailGIF" downloadable="true">
+      <subdef class="thumbnail" name="thumbnailgif" downloadable="true">
         <path>{{datapathweb}}{{basename}}/subdefs</path>
         <size>200</size>
         <mediatype>gif</mediatype>