diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0e5cbc3d..d2af19a9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 
+- Fix nested array stored in DB for readonly dropdown
 - Fix empty dropdown value (-1) on form submission
 - Fix text area fields size and alignment
 - Optimize container loading when there are a large number of entities
diff --git a/inc/container.class.php b/inc/container.class.php
index abcf900b..d1581d8f 100644
--- a/inc/container.class.php
+++ b/inc/container.class.php
@@ -1403,11 +1403,12 @@ public function updateFieldsValues($data, $itemtype, $massiveaction = false)
                     // Add new values to existing ones
                     $existing_values = json_decode($obj->fields[$field_name] ?? '[]', true);
                     $new_values      = is_array($data[$field_name]) ? $data[$field_name] : [$data[$field_name]];
+                    $new_values      = $this->flattenScalars($new_values);
                     $data[$field_name] = json_encode(array_values(array_unique(array_merge($existing_values, $new_values))));
 
                 } else {
                     $value = $data[$field_name];
-                    $value = is_array($value) ? $value : [];
+                    $value = is_array($value) ? $this->flattenScalars($value) : [];
                     $data[$field_name] = json_encode($value);
                 }
             } elseif (array_key_exists('_' . $field_name . '_defined', $data)) {
@@ -1956,6 +1957,29 @@ public static function preItem(CommonDBTM $item)
         return false;
     }
 
+    /**
+     * Flatten a one-level-deep array of mixed scalars/arrays into a flat array of scalars.
+     * Guards against nested arrays produced when a readonly multiple-dropdown field submits
+     * with a doubly-bracketed name (e.g. foo[][][]).
+     */
+    private function flattenScalars(array $values): array
+    {
+        $flat = [];
+        foreach ($values as $v) {
+            if (is_array($v)) {
+                foreach ($v as $inner) {
+                    if (is_scalar($inner)) {
+                        $flat[] = $inner;
+                    }
+                }
+            } elseif (is_scalar($v)) {
+                $flat[] = $v;
+            }
+        }
+
+        return $flat;
+    }
+
     /**
      * Populates fields data from item
      *
diff --git a/inc/field.class.php b/inc/field.class.php
index 6ff05e1d..bd1d4205 100644
--- a/inc/field.class.php
+++ b/inc/field.class.php
@@ -1283,6 +1283,18 @@ public static function prepareHtmlFields(
                 $value = is_array($decoded) ? $decoded : [];
             }
 
+            if ($field['multiple'] && is_array($value)) {
+                // Flatten any nested arrays caused by corrupted DB data (double-encoded values)
+                // so that Dropdown::show() always receives a flat list of scalars.
+                $value = array_values(array_filter(
+                    array_merge(...array_map(
+                        static fn($v) => is_array($v) ? array_values($v) : [$v],
+                        $value,
+                    )),
+                    is_scalar(...),
+                ));
+            }
+
             $field['value'] = $value;
         }