--- a/xml/en/docs/http/ngx_http_realip_module.xml
+++ b/xml/en/docs/http/ngx_http_realip_module.xml
@@ -38,15 +38,20 @@ real_ip_header   X-Real-IP;
 <section id="directives" name="Directives">
 
 <directive name="set_real_ip_from">
-<syntax><value>address</value> | <value>CIDR</value></syntax>
+<syntax>
+    <value>address</value> |
+    <value>CIDR</value> |
+    <literal>unix:</literal></syntax>
 <default/>
 <context>http</context>
 <context>server</context>
 <context>location</context>
 
 <para>
-Describes trusted addresses that are known to send correct
+Describes trusted IPv4 addresses that are known to send correct
 replacement addresses.
+If the special value <literal>unix:</literal> is specified,
+all UNIX-domain sockets will be trusted.
 </para>
 
 </directive>