diff --git a/src/Glpi/CustomObject/AbstractDefinition.php b/src/Glpi/CustomObject/AbstractDefinition.php
index 459aaa4a0f27..c3b96e2984d0 100644
--- a/src/Glpi/CustomObject/AbstractDefinition.php
+++ b/src/Glpi/CustomObject/AbstractDefinition.php
@@ -434,7 +434,11 @@ protected function prepareInput(array $input): array|bool
         $has_errors = false;
 
         if (array_key_exists('system_name', $input)) {
-            if (!is_string($input['system_name']) || preg_match('/^[a-z]+$/i', $input['system_name']) !== 1) {
+            // 1. Must start with a letter.
+            // 2. Must contain only letters or numbers.
+            $system_name_pattern = '/^[a-z][a-z0-9]*$/i';
+
+            if (!is_string($input['system_name']) || preg_match($system_name_pattern, $input['system_name']) !== 1) {
                 Session::addMessageAfterRedirect(
                     htmlescape(sprintf(
                         __('The following field has an incorrect value: "%s".'),
diff --git a/src/Glpi/Search/Provider/SQLProvider.php b/src/Glpi/Search/Provider/SQLProvider.php
index 606c808190bb..8f9c97a9e9e8 100644
--- a/src/Glpi/Search/Provider/SQLProvider.php
+++ b/src/Glpi/Search/Provider/SQLProvider.php
@@ -4789,15 +4789,10 @@ public static function constructData(array &$data, $onlycount = false)
 
                 // Parse data
                 foreach ($newrow['raw'] as $key => $val) {
-                    if (preg_match('/ITEM(_(\w[^\d]+))?_(\d+)(_(.+))?/', $key, $matches)) {
-                        $j = $matches[3];
-                        if (isset($matches[2]) && !empty($matches[2])) {
-                            $j = $matches[2] . '_' . $matches[3];
-                        }
-                        $fieldname = 'name';
-                        if (isset($matches[5])) {
-                            $fieldname = $matches[5];
-                        }
+                    $matches = [];
+                    if (preg_match('/^ITEM(_(?<itemtype>[a-z]\w*))?_(?<num>\d+)(_(?<fieldname>.+))?$/i', $key, $matches)) {
+                        $j = (isset($matches['itemtype']) ? $matches['itemtype'] . '_' : '') . $matches['num'];
+                        $fieldname = $matches['fieldname'] ?? 'name';
 
                         // No Group_concat case
                         if ($fieldname == 'content' || !is_string($val) || strpos($val, \Search::LONGSEP) === false) {
diff --git a/templates/pages/admin/customobjects/main.html.twig b/templates/pages/admin/customobjects/main.html.twig
index 459662ff7a25..0fd375b3a872 100644
--- a/templates/pages/admin/customobjects/main.html.twig
+++ b/templates/pages/admin/customobjects/main.html.twig
@@ -128,30 +128,38 @@
         </script>
     {% endif %}
     <script type="module">
-        $('#mainformtable input[name="system_name"]').on('input', () => {
+        $('#mainformtable input[name="system_name"]').on('change', () => {
             if ($('input[name="system_name"]').val() === '') {
                 $('input[name="system_name"]').data('manually_changed', false);
             } else {
                 $('input[name="system_name"]').data('manually_changed', true);
             }
         });
-        function autoUpdateNameField() {
-            if ({{ not item.isNewItem() ? 'true' : 'false' }} || $('#mainformtable input[name="system_name"]').data('manually_changed')) {
-                return;
-            }
+        $('#mainformtable input[name="system_name"]').on('input', () => {
             const reserved_names = {{ reserved_system_names|json_encode()|raw }}.map((n) => n.toLowerCase());
             const existing_names = {{ existing_system_names|json_encode()|raw }}.map((n) => n.toLowerCase());
-            $('#mainformtable input[name="system_name"]').val(
-                $('#mainformtable input[name="label"]').val().normalize('NFD').replace(/[^a-z]/gi, '')
-            );
             const system_name = $('#mainformtable input[name="system_name"]').val().toLowerCase();
+
             if (reserved_names.includes(system_name) || system_name.endsWith('type') || system_name.endsWith('model')) {
                 $('#mainformtable input[name="system_name"]').get(0).setCustomValidity(__('The system name is a reserved name. Please enter a different label or manually change the system name.'));
             } else if (existing_names.includes(system_name)) {
                 $('#mainformtable input[name="system_name"]').get(0).setCustomValidity(__('The system name is already in use. Please enter a different label or manually change the system name.'));
+            } else if (/^[a-z][a-z0-9]*$/i.test(system_name) === false) {
+                {# See pattern used in \Glpi\CustomObject\AbstractDefinition::prepareInput() #}
+                $('#mainformtable input[name="system_name"]').get(0).setCustomValidity(__('The system name is invalid. It must start with a letter and contain only alphanumeric chars.'));
             } else {
                 $('#mainformtable input[name="system_name"]').get(0).setCustomValidity('');
             }
+        });
+        function autoUpdateNameField() {
+            if ({{ not item.isNewItem() ? 'true' : 'false' }} || $('#mainformtable input[name="system_name"]').data('manually_changed')) {
+                return;
+            }
+
+            $('#mainformtable input[name="system_name"]').val(
+                $('#mainformtable input[name="label"]').val().normalize('NFD').replace(/[^a-z0-9]/gi, '')
+            );
+            $('#mainformtable input[name="system_name"]').trigger('input');
         };
         $('#mainformtable input[name="label"]').on('input', () => {
             autoUpdateNameField();