diff --git a/lib/Doctrine/ORM/Query/AST/InExpression.php b/lib/Doctrine/ORM/Query/AST/InExpression.php
index 9d0a8b54e..cefb450cf 100644
--- a/lib/Doctrine/ORM/Query/AST/InExpression.php
+++ b/lib/Doctrine/ORM/Query/AST/InExpression.php
@@ -45,7 +45,7 @@ class InExpression extends Node
     public $literals = array();
 
     /**
-     * @var Subselect|null
+     * @var array<Subselect>|null
      */
     public $subselect;
 
diff --git a/lib/Doctrine/ORM/Query/Lexer.php b/lib/Doctrine/ORM/Query/Lexer.php
index d5721a735..69f8b9cbe 100644
--- a/lib/Doctrine/ORM/Query/Lexer.php
+++ b/lib/Doctrine/ORM/Query/Lexer.php
@@ -109,6 +109,7 @@ class Lexer extends \Doctrine\Common\Lexer
     const T_WITH                = 155;
     const T_PARTIAL             = 156;
     const T_NEW                 = 157;
+    const T_UNION               = 158;
 
     /**
      * Creates a new query scanner object.
diff --git a/lib/Doctrine/ORM/Query/Parser.php b/lib/Doctrine/ORM/Query/Parser.php
index 695e7ed10..4d8ae92b6 100644
--- a/lib/Doctrine/ORM/Query/Parser.php
+++ b/lib/Doctrine/ORM/Query/Parser.php
@@ -3063,7 +3063,11 @@ class Parser
         $this->match(Lexer::T_OPEN_PARENTHESIS);
 
         if ($this->lexer->isNextToken(Lexer::T_SELECT)) {
-            $inExpression->subselect = $this->Subselect();
+            $inExpression->subselect = [$this->Subselect()];
+            while ($this->lexer->isNextToken(Lexer::T_UNION)) {
+                $this->match(Lexer::T_UNION);
+                $inExpression->subselect[] = $this->Subselect();
+            }
         } else {
             $literals = array();
             $literals[] = $this->InParameter();
diff --git a/lib/Doctrine/ORM/Query/SqlWalker.php b/lib/Doctrine/ORM/Query/SqlWalker.php
index 5ed7adee4..b8b5a0c32 100644
--- a/lib/Doctrine/ORM/Query/SqlWalker.php
+++ b/lib/Doctrine/ORM/Query/SqlWalker.php
@@ -2048,7 +2048,7 @@ class SqlWalker implements TreeWalker
         $sql = $this->walkArithmeticExpression($inExpr->expression) . ($inExpr->not ? ' NOT' : '') . ' IN (';
 
         $sql .= ($inExpr->subselect)
-            ? $this->walkSubselect($inExpr->subselect)
+            ? implode(' UNION ', array_map(function ($subselect) {return $this->walkSubselect($subselect);}, $inExpr->subselect))
             : implode(', ', array_map(array($this, 'walkInParameter'), $inExpr->literals));
 
         $sql .= ')';