diff --git a/lib/Doctrine/ORM/Query/Expr/Base.php b/lib/Doctrine/ORM/Query/Expr/Base.php
index beac2bb9c..975d450cd 100644
--- a/lib/Doctrine/ORM/Query/Expr/Base.php
+++ b/lib/Doctrine/ORM/Query/Expr/Base.php
@@ -57,7 +57,7 @@ abstract class Base
 
     public function add($arg)
     {
-        if ( $arg !== null ) {
+        if ( $arg !== null || ($arg instanceof self && $arg->count() > 0) ) {
             // If we decide to keep Expr\Base instances, we can use this check
             if ( ! is_string($arg)) {
                 $class = get_class($arg);