diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 49f81676712..4da26a6cba3 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -4326,7 +4326,8 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
          or that the parameters all use the default format (text);
          or one, in which case the specified format code is applied
          to all parameters; or it can equal the actual number of
-         parameters.
+         parameters.  This is an unsigned 16-bit integer, so the
+         maximum number of parameter format codes is 65535.
         </para>
        </listitem>
       </varlistentry>
@@ -4347,6 +4348,8 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
         <para>
          The number of parameter values that follow (possibly zero).
          This must match the number of parameters needed by the query.
+         This is an unsigned 16-bit integer, so the maximum number of
+         parameters is 65535.
         </para>
        </listitem>
       </varlistentry>
@@ -4397,7 +4400,9 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
          (text);
          or one, in which case the specified format code is applied
          to all result columns (if any); or it can equal the actual
-         number of result columns of the query.
+         number of result columns of the query.  This is an unsigned
+         16-bit integer, so the maximum number of result-column format
+         codes is 65535.
         </para>
        </listitem>
       </varlistentry>