diff --git a/source/reference/operator/type.txt b/source/reference/operator/type.txt
index 96914d74f09..43c9d9d6f08 100644
--- a/source/reference/operator/type.txt
+++ b/source/reference/operator/type.txt
@@ -54,6 +54,7 @@ $type
    Object                       3
    Array                        4
    Binary data                  5
+   undefined                    6
    Object id                    7
    Boolean                      8
    Date                         9