diff --git a/MysqliDb.php b/MysqliDb.php
index f64c00a0..2b2d6600 100644
--- a/MysqliDb.php
+++ b/MysqliDb.php
@@ -1731,7 +1731,7 @@ public static function subQuery($subQueryAlias = "")
     public function copy()
     {
         $copy = unserialize(serialize($this));
-        $copy->_mysqli = $this->_mysqli;
+        $copy->_mysqli = null;
         return $copy;
     }
 
diff --git a/tests/mysqliDbTests.php b/tests/mysqliDbTests.php
index f1fa9efa..cc993391 100644
--- a/tests/mysqliDbTests.php
+++ b/tests/mysqliDbTests.php
@@ -360,6 +360,8 @@ function createTable ($name, $data) {
     echo "copy with subquery count failed";
     exit;
 }
+unset ($cnt);
+
 $data = $db->get('users');
 if (count($data) != 3) {
     echo "copy with subquery data count failed";