diff --git a/docs/reference/commandline/dockerd.md b/docs/reference/commandline/dockerd.md
index 2ac35680ea..580c2209fe 100644
--- a/docs/reference/commandline/dockerd.md
+++ b/docs/reference/commandline/dockerd.md
@@ -130,6 +130,8 @@ by the `dockerd` command line:
   unsuitable for Docker.
 * `DOCKER_RAMDISK` If set this will disable 'pivot_root'.
 * `DOCKER_TMPDIR` Location for temporary Docker files.
+* `MOBY_DISABLE_PIGZ` Do not use [`unpigz`](https://linux.die.net/man/1/pigz) to
+  decompress layers in parallel when pulling images, even if it is installed.
 
 ## Examples