diff --git a/lib/Doctrine/ORM/Query/Expr.php b/lib/Doctrine/ORM/Query/Expr.php
index 35130fd89..e071d325e 100644
--- a/lib/Doctrine/ORM/Query/Expr.php
+++ b/lib/Doctrine/ORM/Query/Expr.php
@@ -470,9 +470,13 @@ class Expr
      * @param integer $len Length of crop. May accept negative values.
      * @return Expr\Func
      */
-    public function substring($x, $from, $len)
+    public function substring($x, $from, $len = null)
     {
-        return new Expr\Func('SUBSTRING', array($x, $from, $len));
+        $args = array($x, $from);
+        if (null !== $len) {
+            $args[] = $len;
+        }
+        return new Expr\Func('SUBSTRING', $args);
     }
 
     /**
diff --git a/tests/Doctrine/Tests/ORM/Query/ExprTest.php b/tests/Doctrine/Tests/ORM/Query/ExprTest.php
index 60449e5b9..5bf5b06b5 100644
--- a/tests/Doctrine/Tests/ORM/Query/ExprTest.php
+++ b/tests/Doctrine/Tests/ORM/Query/ExprTest.php
@@ -185,6 +185,15 @@ class ExprTest extends \Doctrine\Tests\OrmTestCase
         $this->assertEquals('SUBSTRING(a.title, 0, 25)', (string) $this->_expr->substring('a.title', 0, 25));
     }
 
+    /**
+     * @group regression
+     * @group DDC-612
+     */
+    public function testSubstringExprAcceptsTwoArguments()
+    {
+        $this->assertEquals('SUBSTRING(a.title, 0)', (string) $this->_expr->substring('a.title', 5));
+    }
+
     public function testLowerExpr()
     {
         $this->assertEquals('LOWER(u.first_name)', (string) $this->_expr->lower('u.first_name'));