diff --git a/README.md b/README.md
index 858f74a..551c22f 100644
--- a/README.md
+++ b/README.md
@@ -256,6 +256,7 @@ A custom `[section]` has the following options. We're calling them locals most o
     ports = 
     proto =
     ```
+  * Protocol strings `icmpv6` and `icmp` are treated specially. You can use either one as your `proto =`, UFS will internally automatically use `icmpv6` for `ip6tables` and will use `icmp` for `iptables` rules.
 
 * `state`, __*optional*__, defaults to `NEW`: Comma-separated list of connection tracking states against which a packet is matched. Most of the time your rules will want to use the default `NEW`. The final `DROP` rule present in the example `config.ini` file at [examples/config.ini.example](examples/config.ini.example) is one occasion where you'll want to deviate and unset `state` to an empty value. See ["state" extension man page in iptables docs](https://ipset.netfilter.org/iptables-extensions.man.html#lbCC) for reference.