diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index d67212b..844d4a9 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -5754,11 +5754,12 @@ int PQputline(PGconn *conn,
        <para>
         Before <productname>PostgreSQL</productname> protocol 3.0, it was necessary
         for the application to explicitly send the two characters
-        <literal>\.</literal> as a final line to indicate to the server that it had
-        finished sending <command>COPY</command> data.  While this still works, it is deprecated and the
-        special meaning of <literal>\.</literal> can be expected to be removed in a
-        future release.  It is sufficient to call <function>PQendcopy</function> after
-        having sent the actual data.
+        <literal>\.</literal> as a final line to indicate to the server that
+        the application had finished sending <command>COPY</command> data.
+        While this still works, it is deprecated and the special meaning
+        of <literal>\.</literal> will be removed in a future release.  It is
+        sufficient to call <function>PQendcopy</function> after having sent
+        the actual data.
        </para>
       </note>
      </listitem>
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 46d7e19..fda989b 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1154,6 +1154,20 @@ SELCT 1/0;
     (if successful) or ErrorResponse (if not).
    </para>
 
+   <note>
+     <para>
+       Before <productname>PostgreSQL</productname> protocol 3.0, it was necessary
+       for the application to explicitly send the two characters
+       <literal>\.</literal> as a final line to indicate to the server that
+       the application had finished sending <command>COPY</command> data.
+       Programs implementing <command>COPY</command> in protocol 3.0
+       including <productname>PostgreSQL</productname> need to check and
+       ignore
+       <literal>\.</literal> just before COPYDone message for backward
+       compatibility sake. This requirement will be removed in the future.
+     </para>
+   </note>
+
    <para>
     In the event of a backend-detected error during copy-in mode (including
     receipt of a CopyFail message), the backend will issue an ErrorResponse