diff --git a/api/address.proto b/api/address.proto
index 7fbb42b17..c986f0cf7 100644
--- a/api/address.proto
+++ b/api/address.proto
@@ -44,6 +44,12 @@ message SocketAddress {
   // should be set for resolution other than DNS. If the address is a concrete
   // IP address, no resolution will occur.
   string resolver_name = 5;
+
+  // When binding to an IPv6 address above, this enables `IPv4 compatibity
+  // <https://tools.ietf.org/html/rfc3493#page-11>`_. Binding to ``::`` will
+  // allow both IPv4 and IPv6 connections, with peer IPv4 addresses mapped into
+  // IPv6 space as ``::FFFF:<IPv4-address>``.
+  bool ipv4_compat = 6;
 }
 
 message BindConfig {