diff --git a/doc/src/sgml/ecpg.sgml b/doc/src/sgml/ecpg.sgml
index 0fef9bfcbe..c4412ba99c 100644
--- a/doc/src/sgml/ecpg.sgml
+++ b/doc/src/sgml/ecpg.sgml
@@ -199,6 +199,13 @@ EXEC SQL CONNECT TO <replaceable>target</replaceable> <optional>AS <replaceable>
    any <replaceable>keyword</replaceable> or <replaceable>value</replaceable>,
    though not within or after one.  Note that there is no way to
    write <literal>&amp;</literal> within a <replaceable>value</replaceable>.
+
+   Also note that if you want to specify the socket directory
+   for Unix-domain communications, an option <replaceable>host=</replaceable>
+   and single-quoted string must be used.
+   The notation rule is almost the same as libpq's one,
+   but the IPv6 address cannot be used here.
+
   </para>
 
   <para>