diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/Flag.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/Flag.php
new file mode 100644
index 0000000000..42862eab62
--- /dev/null
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/Flag.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Alchemy\Phrasea\SearchEngine\Elastic\AST;
+
+use Assert\Assertion;
+
+class Flag
+{
+    private $name;
+
+    public function __construct($name)
+    {
+        Assertion::string($name);
+        $this->name = $name;
+    }
+
+    public function getName()
+    {
+        return $this->name;
+    }
+}
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FlagStatement.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FlagStatement.php
index fd8857632f..8b1866862a 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FlagStatement.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FlagStatement.php
@@ -2,9 +2,11 @@
 
 namespace Alchemy\Phrasea\SearchEngine\Elastic\AST;
 
-use Assert\Assertion;
+use Alchemy\Phrasea\SearchEngine\Elastic\Exception\QueryException;
 use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryContext;
+use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Flag as FlagStructure;
 use Alchemy\Phrasea\SearchEngine\Elastic\RecordHelper;
+use Assert\Assertion;
 
 class FlagStatement extends Node
 {
@@ -21,12 +23,14 @@ class FlagStatement extends Node
 
     public function buildQuery(QueryContext $context)
     {
-        // TODO Ensure flag exists
-        $key = RecordHelper::normalizeFlagKey($this->name);
-        $field = sprintf('flags.%s', $key);
+        $name = FlagStructure::normalizeName($this->name);
+        $flag = $context->getFlag($name);
+        if (!$flag) {
+            throw new QueryException(sprintf('Flag "%s" does not exist', $this->name));
+        }
         return [
             'term' => [
-                $field => $this->set
+                $flag->getIndexField() => $this->set
             ]
         ];
     }
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticSearchEngine.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticSearchEngine.php
index e427f11e05..e5a0a02008 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticSearchEngine.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/ElasticSearchEngine.php
@@ -19,6 +19,7 @@ use Alchemy\Phrasea\SearchEngine\Elastic\Search\AggregationHelper;
 use Alchemy\Phrasea\SearchEngine\Elastic\Search\FacetsResponse;
 use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryCompiler;
 use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryContext;
+use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Flag;
 use Alchemy\Phrasea\SearchEngine\Elastic\Structure\LimitedStructure;
 use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Structure;
 use Alchemy\Phrasea\SearchEngine\SearchEngineInterface;
@@ -566,7 +567,7 @@ class ElasticSearchEngine implements SearchEngineInterface
             $databoxId = $databox->get_sbas_id();
             $statusStructure = $databox->getStatusStructure();
             foreach($statusStructure as $bit => $status) {
-                $flags[$databoxId][$bit] = RecordHelper::normalizeFlagKey($status['labelon']);
+                $flags[$databoxId][$bit] = Flag::normalizeName($status['labelon']);
             }
         }
 
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Exception/StructureException.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Exception/StructureException.php
new file mode 100644
index 0000000000..7d713605f9
--- /dev/null
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Exception/StructureException.php
@@ -0,0 +1,16 @@
+<?php
+
+/*
+ * This file is part of Phraseanet
+ *
+ * (c) 2005-2014 Alchemy
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Alchemy\Phrasea\SearchEngine\Elastic\Exception;
+
+class StructureException extends Exception
+{
+}
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/Record/Hydrator/CoreHydrator.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/Record/Hydrator/CoreHydrator.php
index c89a254148..135cf854e8 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/Record/Hydrator/CoreHydrator.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/Record/Hydrator/CoreHydrator.php
@@ -39,6 +39,7 @@ class CoreHydrator implements HydratorInterface
         // Some casting
         $record['record_id'] = (int) $record['record_id'];
         $record['collection_id'] = (int) $record['collection_id'];
+        $record['flags_bitfield'] = (int) $record['flags_bitfield'];
         // Some identifiers
         $record['id'] = $this->helper->getUniqueRecordId($this->databox_id, $record['record_id']);
         $record['base_id'] = $this->helper->getUniqueCollectionId($this->databox_id, $record['collection_id']);
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/Record/Hydrator/FlagHydrator.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/Record/Hydrator/FlagHydrator.php
new file mode 100644
index 0000000000..135282edbb
--- /dev/null
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/Record/Hydrator/FlagHydrator.php
@@ -0,0 +1,62 @@
+<?php
+
+/*
+ * This file is part of Phraseanet
+ *
+ * (c) 2005-2014 Alchemy
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Hydrator;
+
+use Alchemy\Phrasea\SearchEngine\Elastic\Exception\StructureException;
+use Alchemy\Phrasea\SearchEngine\Elastic\RecordHelper;
+use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Flag;
+use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Structure;
+use Alchemy\Phrasea\SearchEngine\SearchEngineInterface;
+use databox;
+
+class FlagHydrator implements HydratorInterface
+{
+    public function __construct(Structure $structure, databox $databox)
+    {
+        $this->field_names_map = self::buildFieldNamesMap($structure, $databox);
+    }
+
+    private static function buildFieldNamesMap(Structure $structure, databox $databox)
+    {
+        $names_map = [];
+        foreach ($structure->getAllFlags() as $name => $flag) {
+            $bit = $flag->getBitPositionInDatabox($databox);
+            if ($bit === null) {
+                continue;
+            }
+            if (isset($names_map[$bit])) {
+                throw new StructureException(sprintf('Duplicated flag for bit %d', $bit));
+            }
+            $names_map[$bit] = $name;
+        }
+        return $names_map;
+    }
+
+    public function hydrateRecords(array &$records)
+    {
+        foreach ($records as &$record) {
+            if (isset($record['flags_bitfield'])) {
+                $record['flags'] = $this->bitfieldToFlagsMap($record['flags_bitfield']);
+                var_dump($record['flags_bitfield'], $record['flags']);
+            }
+        }
+    }
+
+    private function bitfieldToFlagsMap($bitfield)
+    {
+        $flags = [];
+        foreach ($this->field_names_map as $position => $name) {
+            $flags[$name] = \databox_status::bitIsSet($bitfield, $position);
+        }
+        return $flags;
+    }
+}
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/RecordIndexer.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/RecordIndexer.php
index 6650a68a53..f7bbf8e5aa 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/RecordIndexer.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Indexer/RecordIndexer.php
@@ -20,6 +20,7 @@ use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Delegate\RecordListFetch
 use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Delegate\ScheduledFetcherDelegate;
 use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Fetcher;
 use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Hydrator\CoreHydrator;
+use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Hydrator\FlagHydrator;
 use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Hydrator\MetadataHydrator;
 use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Hydrator\SubDefinitionHydrator;
 use Alchemy\Phrasea\SearchEngine\Elastic\Indexer\Record\Hydrator\ThesaurusHydrator;
@@ -143,6 +144,7 @@ class RecordIndexer
             new CoreHydrator($databox->get_sbas_id(), $databox->get_viewname(), $this->helper),
             new TitleHydrator($connection),
             new MetadataHydrator($connection, $this->structure, $this->helper),
+            new FlagHydrator($this->structure, $databox),
             new ThesaurusHydrator($this->structure, $this->thesaurus, $candidateTerms),
             new SubDefinitionHydrator($connection)
         ), $delegate);
@@ -174,7 +176,7 @@ class RecordIndexer
             $params['id'] = $record['id'];
             unset($record['id']);
             $params['type'] = self::TYPE_NAME;
-            $params['body'] = $this->transform($record);
+            $params['body'] = $record;
             $bulk->index($params);
         }
     }
@@ -307,37 +309,10 @@ class RecordIndexer
     private function getFlagsMapping()
     {
         $mapping = new Mapping();
-
-        foreach ($this->appbox->get_databoxes() as $databox) {
-            foreach ($databox->getStatusStructure() as $bit => $status) {
-                $key = RecordHelper::normalizeFlagKey($status['labelon']);
-                // We only add to mapping new statuses
-                if (!$mapping->has($key)) {
-                    $mapping->add($key, 'boolean');
-                }
-            }
+        foreach ($this->structure->getAllFlags() as $name => $_) {
+            $mapping->add($name, 'boolean');
         }
 
         return $mapping;
     }
-
-    /**
-     * Inspired by ESRecordSerializer
-     *
-     * @todo complete, with all the other transformations
-     * @todo convert this function in a HydratorInterface and inject into fetcher
-     * @param $record
-     */
-    private function transform($record)
-    {
-        $databox = $this->appbox->get_databox($record['databox_id']);
-
-        foreach ($databox->getStatusStructure() as $bit => $status) {
-            $key = RecordHelper::normalizeFlagKey($status['labelon']);
-
-            $record['flags'][$key] = \databox_status::bitIsSet($record['flags_bitfield'], $bit);
-        }
-
-        return $record;
-    }
 }
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/RecordHelper.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/RecordHelper.php
index 73090c4c11..91dc676b10 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/RecordHelper.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/RecordHelper.php
@@ -14,6 +14,7 @@ namespace Alchemy\Phrasea\SearchEngine\Elastic;
 use Alchemy\Phrasea\SearchEngine\Elastic\Exception\MergeException;
 use Alchemy\Phrasea\SearchEngine\Elastic\Mapping;
 use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Field;
+use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Flag;
 use appbox;
 use DateTime;
 use igorw;
@@ -70,11 +71,6 @@ class RecordHelper
         return $this->collectionMap;
     }
 
-    public static function normalizeFlagKey($key)
-    {
-        return StringUtils::slugify($key, '_');
-    }
-
     public static function validateDate($date)
     {
         $d = DateTime::createFromFormat(Mapping::DATE_FORMAT_CAPTION_PHP, $date);
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryContext.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryContext.php
index 5aff671a91..a9362624db 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryContext.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryContext.php
@@ -6,6 +6,7 @@ use Alchemy\Phrasea\SearchEngine\Elastic\Exception\QueryException;
 use Alchemy\Phrasea\SearchEngine\Elastic\Mapping;
 use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Field;
 use Alchemy\Phrasea\SearchEngine\Elastic\AST\Field as ASTField;
+use Alchemy\Phrasea\SearchEngine\Elastic\AST\Flag;
 use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Structure;
 
 /**
@@ -73,11 +74,15 @@ class QueryContext
         if ($name instanceof ASTField) {
             $name = $name->getValue();
         }
-        $field = $this->structure->get($name);
-        if (!$field) {
-            return null;
+        return $this->structure->get($name);
+    }
+
+    public function getFlag($name)
+    {
+        if ($name instanceof Flag) {
+            $name = $name->getName();
         }
-        return $field;
+        return $this->structure->getFlagByName($name);
     }
 
     /**
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php
index c377b83ba0..8649d2e5b7 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php
@@ -86,7 +86,7 @@ class QueryVisitor implements Visit
                 return $this->visitFlagStatementNode($element);
 
             case NodeTypes::FLAG:
-                return $this->visitString($element);
+                return new AST\Flag($this->visitString($element));
 
             case NodeTypes::DATABASE:
                 return $this->visitDatabaseNode($element);
@@ -275,9 +275,13 @@ class QueryVisitor implements Visit
         if ($node->getChildrenNumber() !== 2) {
             throw new \Exception('Flag statement can only have 2 childs.');
         }
+        $flag = $node->getChild(0)->accept($this);
+        if (!$flag instanceof AST\Flag) {
+            throw new \Exception('Flag statement key must be a flag node.');
+        }
 
         return new AST\FlagStatement(
-            $node->getChild(0)->accept($this),
+            $flag->getName(),
             $this->visitBoolean($node->getChild(1))
         );
     }
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Flag.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Flag.php
new file mode 100644
index 0000000000..c1eeac0577
--- /dev/null
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Flag.php
@@ -0,0 +1,54 @@
+<?php
+
+namespace Alchemy\Phrasea\SearchEngine\Elastic\Structure;
+
+use Alchemy\Phrasea\SearchEngine\Elastic\StringUtils;
+use Assert\Assertion;
+use InvalidArgumentException;
+
+class Flag
+{
+    private $name;
+
+    public static function createFromLegacyStatus(array $status)
+    {
+        if (!isset($status['labelon'])) {
+            throw new InvalidArgumentException('Status array must contain the "labelon" key.');
+        }
+        return new self(self::normalizeName($status['labelon']));
+    }
+
+    public function __construct($name)
+    {
+        Assertion::string($name);
+        $this->name = $name;
+    }
+
+    public function getName()
+    {
+        return $this->name;
+    }
+
+    public function getIndexField()
+    {
+        return sprintf('flags.%s', $this->name);
+    }
+
+    public static function normalizeName($key)
+    {
+        return StringUtils::slugify($key, '_');
+    }
+
+    /*
+     * TODO: Rewrite to have all data injected at construct time in createFromLegacyStatus()
+     */
+    public function getBitPositionInDatabox(\databox $databox)
+    {
+        foreach ($databox->getStatusStructure() as $bit => $status) {
+            $candidate_name = self::normalizeName($status['labelon']);
+            if ($candidate_name === $this->name) {
+                return (int) $status['bit'];
+            }
+        }
+    }
+}
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/GlobalStructure.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/GlobalStructure.php
index 4bfc5d97fd..57f9fba751 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/GlobalStructure.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/GlobalStructure.php
@@ -3,6 +3,7 @@
 namespace Alchemy\Phrasea\SearchEngine\Elastic\Structure;
 
 use Alchemy\Phrasea\SearchEngine\Elastic\Mapping;
+use Assert\Assertion;
 use DomainException;
 
 final class GlobalStructure implements Structure
@@ -17,6 +18,7 @@ final class GlobalStructure implements Structure
     private $private = array();
     /** @var Field[] */
     private $facets = array();
+    private $flags = array();
 
     /**
      * @param \databox[] $databoxes
@@ -24,17 +26,32 @@ final class GlobalStructure implements Structure
      */
     public static function createFromDataboxes(array $databoxes)
     {
-        $structure = new self();
+        $fields = [];
+        $flags = [];
         foreach ($databoxes as $databox) {
             foreach ($databox->get_meta_structure() as $fieldStructure) {
-                $field = Field::createFromLegacyField($fieldStructure);
-                $structure->add($field);
+                $fields[] = Field::createFromLegacyField($fieldStructure);
+            }
+            foreach ($databox->getStatusStructure() as $status) {
+                $flags[] = Flag::createFromLegacyStatus($status);
             }
         }
-        return $structure;
+        return new self($fields, $flags);
     }
 
-    public function add(Field $field)
+    public function __construct(array $fields, array $flags)
+    {
+        Assertion::allIsInstanceOf($fields, Field::class);
+        Assertion::allIsInstanceOf($flags, Flag::class);
+        foreach ($fields as $field) {
+            $this->add($field);
+        }
+        foreach ($flags as $flag) {
+            $this->flags[$flag->getName()] = $flag;
+        }
+    }
+
+    private function add(Field $field)
     {
         $name = $field->getName();
         if (isset($this->fields[$name])) {
@@ -120,6 +137,17 @@ final class GlobalStructure implements Structure
         throw new DomainException(sprintf('Unknown field "%s".', $name));
     }
 
+    public function getAllFlags()
+    {
+        return $this->flags;
+    }
+
+    public function getFlagByName($name)
+    {
+        return isset($this->flags[$name]) ?
+                     $this->flags[$name] : null;
+    }
+
     /**
      * Returns an array of collections indexed by field name.
      *
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/LimitedStructure.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/LimitedStructure.php
index db0256e105..aa187102d5 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/LimitedStructure.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/LimitedStructure.php
@@ -75,6 +75,16 @@ final class LimitedStructure implements Structure
         return $this->structure->isPrivate($name);
     }
 
+    public function getAllFlags()
+    {
+        return $this->structure->getAllFlags();
+    }
+
+    public function getFlagByName($name)
+    {
+        return $this->structure->getFlagByName($name);
+    }
+
     private function limit(array $fields)
     {
         $allowed_collections = $this->allowedCollections();
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Structure.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Structure.php
index 7b4acf585f..f4d50be9ce 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Structure.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Structure/Structure.php
@@ -24,4 +24,7 @@ interface Structure
      * @throws \DomainException
      */
     public function isPrivate($name);
+
+    public function getAllFlags();
+    public function getFlagByName($name);
 }