diff --git a/README.md b/README.md
index a3ac06e..decfbb3 100644
--- a/README.md
+++ b/README.md
@@ -178,7 +178,7 @@ These are the arguments:
 * `name`: the libvirt name (string, required)
 * `uuid`: the libvirt identifier (UUID string, required)
 * `memory`: amount of RAM (set with `count` (integer) and `unit` (string) attributes, default `{ count = 2; unit = "GiB"; }`)
-* `storage_vol`: source element or path to a QCOW2 volume for storage (set, string or path, required)
+* `storage_vol`: source element or path to a QCOW2 volume for storage, or null (set, string or path, default `null`)
 * `install_vol`: source element or path to an ISO image for an inserted CDROM, or null (set, string or path, default `null`)
 * `virtio_net`: whether to use VirtIO for networking (faster, but may require special guest drivers) (bool, default `false`)
 * `virtio_video`: whether to use VirtIO for graphics (bool, default `true`)
@@ -193,7 +193,7 @@ These are the arguments:
 * `name`: the libvirt name (string, required)
 * `uuid`: the libvirt identifier (UUID string, required)
 * `memory`: amount of RAM (set with `count` (integer) and `unit` (string) attributes, default `{ count = 2; unit = "GiB"; }`)
-* `storage_vol`: source element or path to a QCOW2 volume for storage (set, string or path, required)
+* `storage_vol`: source element or path to a QCOW2 volume for storage, or null (set, string or path, default `null`)
 * `install_vol`: source element or path to an ISO image for an inserted CDROM, or null (set, string or path, default `null`)
 * `virtio_net`: whether to use VirtIO for networking (faster, but may require special guest drivers) (bool, default `false`)
 * `virtio_video`: whether to use VirtIO for graphics (bool, default `true`)
@@ -208,7 +208,7 @@ These are the arguments:
 * `name`: the libvirt name (string, required)
 * `uuid`: the libvirt identifier (UUID string, required)
 * `memory`: amount of RAM (set with `count` (integer) and `unit` (string) attributes, default `{ count = 4; unit = "GiB"; }`)
-* `storage_vol`: source element or path to a QCOW2 volume for storage (set, string or path, required)
+* `storage_vol`: source element or path to a QCOW2 volume for storage, or null (set, string or path, default `null`)
 * `install_vol`: source element or path to an ISO image for an inserted CDROM, or null (set, string or path, default `null`)
 * `virtio_video`: whether to use VirtIO for graphics (bool, default `true`)
 * `virtio_drive`: whether to use VirtIO for the storage device (bool, default `true`)