diff --git a/README.md b/README.md
index 5945f7b..2a03995 100644
--- a/README.md
+++ b/README.md
@@ -211,5 +211,5 @@ Enabling IPv6 allows you to be more easily/natively reached by IPv6 native clien
 
  * `ipv6_enabled`: Set to `true` to enable IPv6 support. Defaults to `false`.
  * `internal_address6`: Optional; if unset, SLAAC is used. Specify a static IPv6 address to bind to `internal_interface`.
- * `internal_subnet6`: Required if `internal_address6` is set. Specify a static IPv6 subnet that is associated to your `internal_interface`.
+ * `internal_mask6`: Required if `internal_address6` is set. Specify a static IPv6 subnet mask (i.e. `64` for a /64) that is associated to your `internal_interface`.
  * `internal_gateway6`: Required if `internal_address6` is set. Specify a static IPv6 gateway that is reachable at your `internal_interface`.