diff --git a/lib/Doctrine/ORM/Query/Expr/Base.php b/lib/Doctrine/ORM/Query/Expr/Base.php
index 28771890c..6eac70a27 100644
--- a/lib/Doctrine/ORM/Query/Expr/Base.php
+++ b/lib/Doctrine/ORM/Query/Expr/Base.php
@@ -86,7 +86,7 @@ abstract class Base
      */
     public function add($arg)
     {
-        if ( $arg !== null || ($arg instanceof self && $arg->count() > 0) ) {
+        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);
diff --git a/tests/Doctrine/Tests/ORM/Query/ExprTest.php b/tests/Doctrine/Tests/ORM/Query/ExprTest.php
index d35944bf8..4d90ea1d8 100644
--- a/tests/Doctrine/Tests/ORM/Query/ExprTest.php
+++ b/tests/Doctrine/Tests/ORM/Query/ExprTest.php
@@ -414,4 +414,18 @@ class ExprTest extends \Doctrine\Tests\OrmTestCase
         $select = new Expr\Select(array('foo', 'bar'));
         $this->assertEquals(array('foo', 'bar'), $select->getParts());
     }
+
+    public function testAddEmpty() {
+        $andExpr = $this->_expr->andx();
+        $andExpr->add($this->_expr->andx());
+        
+        $this->assertEquals(0, $andExpr->count());
+    }
+
+    public function testAddNull() {
+        $andExpr = $this->_expr->andx();
+        $andExpr->add(null);
+        
+        $this->assertEquals(0, $andExpr->count());
+    }
 }