diff --git a/src/Jenssegers/Mongodb/Query/Builder.php b/src/Jenssegers/Mongodb/Query/Builder.php
index 51b1527c9..d5c5b8278 100644
--- a/src/Jenssegers/Mongodb/Query/Builder.php
+++ b/src/Jenssegers/Mongodb/Query/Builder.php
@@ -854,7 +854,7 @@ public function convertKey($id)
     {
         if (is_string($id) && strlen($id) === 24 && ctype_xdigit($id)) {
             return new ObjectID($id);
-        } elseif (strlen($id) === 16 && preg_match('~[^\x20-\x7E\t\r\n]~', $id) > 0) {
+        } elseif (is_string($id) && strlen($id) === 16 && preg_match('~[^\x20-\x7E\t\r\n]~', $id) > 0) {
             return new Binary($id, Binary::TYPE_UUID);
         }