diff --git a/grammar/query.pp b/grammar/query.pp
index 6deea123e3..c68267c356 100644
--- a/grammar/query.pp
+++ b/grammar/query.pp
@@ -31,6 +31,9 @@
 %token  collection      collection
 %token  type            type
 %token  id              id|recordid
+%token  flag_prefix     flag.
+%token  true            true|1
+%token  false           false|0
 %token  word            [^\s()\[\]:<>≤≥=]+
 
 // relative order of precedence is NOT > XOR > AND > OR
@@ -58,9 +61,17 @@ quaternary:
   | ::collection:: ::colon:: string() #collection
   | ::type:: ::colon:: string() #type
   | ::id:: ::colon:: string() #id
+  | ::flag_prefix:: flag() ::colon:: boolean() #flag_statement
   | quinary()
 
 
+#flag:
+  word_or_keyword()+
+
+boolean:
+    <true>
+  | <false>
+
 // Field narrowing
 
 quinary:
@@ -140,6 +151,9 @@ keyword:
   | <collection>
   | <type>
   | <id>
+  | <flag_prefix>
+  | <true>
+  | <false>
 
 symbol:
     <parenthese_>
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FlagStatement.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FlagStatement.php
new file mode 100644
index 0000000000..fd8857632f
--- /dev/null
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FlagStatement.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Alchemy\Phrasea\SearchEngine\Elastic\AST;
+
+use Assert\Assertion;
+use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryContext;
+use Alchemy\Phrasea\SearchEngine\Elastic\RecordHelper;
+
+class FlagStatement extends Node
+{
+    private $name;
+    private $set;
+
+    public function __construct($name, $set)
+    {
+        Assertion::string($name);
+        Assertion::boolean($set);
+        $this->name = $name;
+        $this->set = $set;
+    }
+
+    public function buildQuery(QueryContext $context)
+    {
+        // TODO Ensure flag exists
+        $key = RecordHelper::normalizeFlagKey($this->name);
+        $field = sprintf('flags.%s', $key);
+        return [
+            'term' => [
+                $field => $this->set
+            ]
+        ];
+    }
+
+    public function getTermNodes()
+    {
+        return array();
+    }
+
+    public function __toString()
+    {
+        return sprintf('<flag:%s %s>', $this->name, $this->set ? 'set' : 'cleared');
+    }
+}
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/NodeTypes.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/NodeTypes.php
index 691017938f..2967bafc70 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/NodeTypes.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/NodeTypes.php
@@ -21,6 +21,8 @@ class NodeTypes
     const TERM                = '#thesaurus_term';
     const TEXT                = '#text';
     const CONTEXT             = '#context';
+    const FLAG_STATEMENT      = '#flag_statement';
+    const FLAG                = '#flag';
     const COLLECTION          = '#collection';
     const TYPE                = '#type';
     const DATABASE            = '#database';
@@ -29,4 +31,6 @@ class NodeTypes
     const TOKEN_WORD          = 'word';
     const TOKEN_QUOTED_STRING = 'quoted';
     const TOKEN_RAW_STRING    = 'raw_quoted';
+    const TOKEN_TRUE          = 'true';
+    const TOKEN_FALSE         = 'false';
 }
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php
index 9ce5208dde..c377b83ba0 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/Search/QueryVisitor.php
@@ -82,6 +82,12 @@ class QueryVisitor implements Visit
             case NodeTypes::FIELD:
                 return new AST\Field($this->visitString($element));
 
+            case NodeTypes::FLAG_STATEMENT:
+                return $this->visitFlagStatementNode($element);
+
+            case NodeTypes::FLAG:
+                return $this->visitString($element);
+
             case NodeTypes::DATABASE:
                 return $this->visitDatabaseNode($element);
 
@@ -242,6 +248,8 @@ class QueryVisitor implements Visit
                 }
             } elseif ($node instanceof AST\Node) {
                 $root = new AST\AndExpression($root, $node);
+            } else {
+                throw new \Exception('Unexpected node type inside text node.');
             }
         }
 
@@ -262,6 +270,35 @@ class QueryVisitor implements Visit
         return implode($tokens);
     }
 
+    private function visitFlagStatementNode(TreeNode $node)
+    {
+        if ($node->getChildrenNumber() !== 2) {
+            throw new \Exception('Flag statement can only have 2 childs.');
+        }
+
+        return new AST\FlagStatement(
+            $node->getChild(0)->accept($this),
+            $this->visitBoolean($node->getChild(1))
+        );
+    }
+
+    private function visitBoolean(TreeNode $node)
+    {
+        if (null === $value = $node->getValue()) {
+            throw new \Exception('Boolean node must be a token');
+        }
+        switch ($value['token']) {
+            case NodeTypes::TOKEN_TRUE:
+                return true;
+
+            case NodeTypes::TOKEN_FALSE:
+                return false;
+
+            default:
+                throw new \Exception('Unexpected token for a boolean.');
+        }
+    }
+
     private function visitDatabaseNode(Element $element)
     {
         if ($element->getChildrenNumber() !== 1) {
diff --git a/tests/Alchemy/Tests/Phrasea/SearchEngine/AST/FlagStatementTest.php b/tests/Alchemy/Tests/Phrasea/SearchEngine/AST/FlagStatementTest.php
new file mode 100644
index 0000000000..6a1a2bbbcb
--- /dev/null
+++ b/tests/Alchemy/Tests/Phrasea/SearchEngine/AST/FlagStatementTest.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace Alchemy\Tests\Phrasea\SearchEngine\AST;
+
+use Alchemy\Phrasea\SearchEngine\Elastic\AST\FlagStatement;
+use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryContext;
+
+/**
+ * @group unit
+ * @group searchengine
+ * @group ast
+ */
+class FlagStatementTest extends \PHPUnit_Framework_TestCase
+{
+    public function testSerialization()
+    {
+        $this->assertTrue(method_exists(FlagStatement::class, '__toString'), 'Class does not have method __toString');
+        $node = new FlagStatement('foo', true);
+        $this->assertEquals('<flag:foo set>', (string) $node);
+        $node = new FlagStatement('foo', false);
+        $this->assertEquals('<flag:foo cleared>', (string) $node);
+    }
+
+    public function testQueryBuild()
+    {
+        $query_context = $this->prophesize(QueryContext::class);
+
+        $node = new FlagStatement('foo', true);
+        $query = $node->buildQuery($query_context->reveal());
+
+        $expected = '{
+            "term": {
+                "flags.foo": true
+            }
+        }';
+
+        $this->assertEquals(json_decode($expected, true), $query);
+    }
+}
diff --git a/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv b/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv
index 24e80869d4..d1d237df3f 100644
--- a/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv
+++ b/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv
@@ -78,6 +78,15 @@ id:90 AND foo|(<record_identifier:90> AND <text:"foo">)
 id:90 foo|<text:"id:90 foo">
 recordid:90|<record_identifier:90>
 
+# Flag matcher
+flag.foo:true|<flag:foo set>
+flag.foo:1|<flag:foo set>
+flag.foo:false|<flag:foo cleared>
+flag.foo:0|<flag:foo cleared>
+flag.true:true|<flag:true set>
+flag.foo bar:true|<text:"flag.foo bar:true">
+true|<text:"true">
+
 # Matcher on unknown name --> fulltext
 foo:bar|<text:"foo:bar">