diff --git a/proxy/sshproxy.c b/proxy/sshproxy.c
index ad274d57..d113cb04 100644
--- a/proxy/sshproxy.c
+++ b/proxy/sshproxy.c
@@ -262,20 +262,22 @@ static size_t sshproxy_output(Seat *seat, SeatOutputType type,
                               const void *data, size_t len)
 {
     SshProxy *sp = container_of(seat, SshProxy, seat);
-    if (type == SEAT_OUTPUT_AUTH_BANNER) {
-        if (sp->clientseat) {
-            /*
-             * If we have access to the outer Seat, pass the SSH login
-             * banner on to it.
-             */
-            return seat_output(sp->clientseat, type, data, len);
-        } else {
-            return 0;
-        }
+    bufchain_add(&sp->ssh_to_socket, data, len);
+    try_send_ssh_to_socket(sp);
+    return bufchain_size(&sp->ssh_to_socket);
+}
+
+static size_t sshproxy_banner(Seat *seat, const void *data, size_t len)
+{
+    SshProxy *sp = container_of(seat, SshProxy, seat);
+    if (sp->clientseat) {
+        /*
+         * If we have access to the outer Seat, pass the SSH login
+         * banner on to it.
+         */
+        return seat_banner(sp->clientseat, data, len);
     } else {
-        bufchain_add(&sp->ssh_to_socket, data, len);
-        try_send_ssh_to_socket(sp);
-        return bufchain_size(&sp->ssh_to_socket);
+        return 0;
     }
 }
 
@@ -452,6 +454,7 @@ static const SeatVtable SshProxy_seat_vt = {
     .output = sshproxy_output,
     .eof = sshproxy_eof,
     .sent = sshproxy_sent,
+    .banner = sshproxy_banner,
     .get_userpass_input = sshproxy_get_userpass_input,
     .notify_session_started = sshproxy_notify_session_started,
     .notify_remote_exit = nullseat_notify_remote_exit,
diff --git a/pscp.c b/pscp.c
index 0b091085..13e89812 100644
--- a/pscp.c
+++ b/pscp.c
@@ -67,6 +67,7 @@ static const SeatVtable pscp_seat_vt = {
     .output = pscp_output,
     .eof = pscp_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner_to_stderr,
     .get_userpass_input = filexfer_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = nullseat_notify_remote_exit,
diff --git a/psftp.c b/psftp.c
index e00ebed1..14483569 100644
--- a/psftp.c
+++ b/psftp.c
@@ -48,6 +48,7 @@ static const SeatVtable psftp_seat_vt = {
     .output = psftp_output,
     .eof = psftp_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner_to_stderr,
     .get_userpass_input = filexfer_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = nullseat_notify_remote_exit,
diff --git a/putty.h b/putty.h
index 1d55f91e..4e1f9dde 100644
--- a/putty.h
+++ b/putty.h
@@ -925,7 +925,7 @@ typedef enum SeatInteractionContext {
 } SeatInteractionContext;
 
 typedef enum SeatOutputType {
-    SEAT_OUTPUT_STDOUT, SEAT_OUTPUT_STDERR, SEAT_OUTPUT_AUTH_BANNER
+    SEAT_OUTPUT_STDOUT, SEAT_OUTPUT_STDERR
 } SeatOutputType;
 
 /*
@@ -941,11 +941,10 @@ struct Seat {
 struct SeatVtable {
     /*
      * Provide output from the remote session. 'type' indicates the
-     * type of the output (stdout, stderr or SSH auth banner), which
-     * can be used to split the output into separate message channels,
-     * if the seat wants to handle them differently. But combining the
-     * channels into one is OK too; that's what terminal-window based
-     * seats do.
+     * type of the output (stdout or stderr), which can be used to
+     * split the output into separate message channels, if the seat
+     * wants to handle them differently. But combining the channels
+     * into one is OK too; that's what terminal-window based seats do.
      *
      * The return value is the current size of the output backlog.
      */
@@ -971,6 +970,14 @@ struct SeatVtable {
      */
     void (*sent)(Seat *seat, size_t new_sendbuffer);
 
+    /*
+     * Provide authentication-banner output from the session setup.
+     * End-user Seats can treat this as very similar to 'output', but
+     * intermediate Seats in complex proxying situations will want to
+     * implement this and 'output' differently.
+     */
+    size_t (*banner)(Seat *seat, const void *data, size_t len);
+
     /*
      * Try to get answers from a set of interactive login prompts. The
      * prompts are provided in 'p'.
@@ -1227,6 +1234,8 @@ static inline bool seat_eof(Seat *seat)
 { return seat->vt->eof(seat); }
 static inline void seat_sent(Seat *seat, size_t bufsize)
 { seat->vt->sent(seat, bufsize); }
+static inline size_t seat_banner(Seat *seat, const void *data, size_t len)
+{ return seat->vt->banner(seat, data, len); }
 static inline int seat_get_userpass_input(Seat *seat, prompts_t *p)
 { return seat->vt->get_userpass_input(seat, p); }
 static inline void seat_notify_session_started(Seat *seat)
@@ -1293,10 +1302,10 @@ static inline size_t seat_stderr(Seat *seat, const void *data, size_t len)
 { return seat_output(seat, SEAT_OUTPUT_STDERR, data, len); }
 static inline size_t seat_stderr_pl(Seat *seat, ptrlen data)
 { return seat_output(seat, SEAT_OUTPUT_STDERR, data.ptr, data.len); }
-static inline size_t seat_banner(Seat *seat, const void *data, size_t len)
-{ return seat_output(seat, SEAT_OUTPUT_AUTH_BANNER, data, len); }
+
+/* Alternative API for seat_banner taking a ptrlen */
 static inline size_t seat_banner_pl(Seat *seat, ptrlen data)
-{ return seat_output(seat, SEAT_OUTPUT_AUTH_BANNER, data.ptr, data.len); }
+{ return seat->vt->banner(seat, data.ptr, data.len); }
 
 /* In the utils subdir: print a message to the Seat which can't be
  * spoofed by server-supplied auth-time output such as SSH banners */
@@ -1313,6 +1322,8 @@ size_t nullseat_output(
     Seat *seat, SeatOutputType type, const void *data, size_t len);
 bool nullseat_eof(Seat *seat);
 void nullseat_sent(Seat *seat, size_t bufsize);
+size_t nullseat_banner(Seat *seat, const void *data, size_t len);
+size_t nullseat_banner_to_stderr(Seat *seat, const void *data, size_t len);
 int nullseat_get_userpass_input(Seat *seat, prompts_t *p);
 void nullseat_notify_session_started(Seat *seat);
 void nullseat_notify_remote_exit(Seat *seat);
diff --git a/ssh/server.c b/ssh/server.c
index 63a68f62..724abaf4 100644
--- a/ssh/server.c
+++ b/ssh/server.c
@@ -108,6 +108,7 @@ static const SeatVtable server_seat_vt = {
     .output = nullseat_output,
     .eof = nullseat_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner,
     .get_userpass_input = nullseat_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = nullseat_notify_remote_exit,
diff --git a/ssh/sesschan.c b/ssh/sesschan.c
index 6951edc4..56ee37e1 100644
--- a/ssh/sesschan.c
+++ b/ssh/sesschan.c
@@ -187,6 +187,7 @@ static const SeatVtable sesschan_seat_vt = {
     .output = sesschan_seat_output,
     .eof = sesschan_seat_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner,
     .get_userpass_input = nullseat_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = sesschan_notify_remote_exit,
@@ -614,11 +615,6 @@ static size_t sesschan_seat_output(
     Seat *seat, SeatOutputType type, const void *data, size_t len)
 {
     sesschan *sess = container_of(seat, sesschan, seat);
-
-    /* We don't expect anything but stdout and stderr to come here,
-     * because the pty backend doesn't generate auth banners */
-    assert(type != SEAT_OUTPUT_AUTH_BANNER);
-
     return sshfwd_write_ext(sess->c, type == SEAT_OUTPUT_STDERR, data, len);
 }
 
diff --git a/unix/plink.c b/unix/plink.c
index 524e4545..dee0cbec 100644
--- a/unix/plink.c
+++ b/unix/plink.c
@@ -391,6 +391,7 @@ static const SeatVtable plink_seat_vt = {
     .output = plink_output,
     .eof = plink_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner_to_stderr,
     .get_userpass_input = plink_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = nullseat_notify_remote_exit,
diff --git a/unix/window.c b/unix/window.c
index c3ddb515..c5894ffa 100644
--- a/unix/window.c
+++ b/unix/window.c
@@ -390,6 +390,7 @@ static const SeatVtable gtk_seat_vt = {
     .output = gtk_seat_output,
     .eof = gtk_seat_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner_to_stderr,
     .get_userpass_input = gtk_seat_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = gtk_seat_notify_remote_exit,
diff --git a/utils/nullseat.c b/utils/nullseat.c
index 19fad59d..a53f563e 100644
--- a/utils/nullseat.c
+++ b/utils/nullseat.c
@@ -8,6 +8,9 @@ size_t nullseat_output(
     Seat *seat, SeatOutputType type, const void *data, size_t len) {return 0;}
 bool nullseat_eof(Seat *seat) { return true; }
 void nullseat_sent(Seat *seat, size_t bufsize) {}
+size_t nullseat_banner(Seat *seat, const void *data, size_t len) {return 0;}
+size_t nullseat_banner_to_stderr(Seat *seat, const void *data, size_t len)
+{ return seat_output(seat, SEAT_OUTPUT_STDERR, data, len); }
 int nullseat_get_userpass_input(Seat *seat, prompts_t *p) { return 0; }
 void nullseat_notify_session_started(Seat *seat) {}
 void nullseat_notify_remote_exit(Seat *seat) {}
diff --git a/utils/tempseat.c b/utils/tempseat.c
index f877dd1d..eac10f8d 100644
--- a/utils/tempseat.c
+++ b/utils/tempseat.c
@@ -224,6 +224,11 @@ static int tempseat_get_userpass_input(Seat *seat, prompts_t *p)
     unreachable("get_userpass_input should never be called on TempSeat");
 }
 
+static size_t tempseat_banner(Seat *seat, const void *data, size_t len)
+{
+    unreachable("banner should never be called on TempSeat");
+}
+
 static int tempseat_confirm_ssh_host_key(
     Seat *seat, const char *host, int port, const char *keytype,
     char *keystr, const char *keydisp, char **key_fingerprints, bool mismatch,
@@ -299,6 +304,7 @@ static const struct SeatVtable tempseat_vt = {
     .output = tempseat_output,
     .eof = tempseat_eof,
     .sent = nullseat_sent,
+    .banner = tempseat_banner,
     .get_userpass_input = tempseat_get_userpass_input,
     .notify_session_started = tempseat_notify_session_started,
     .notify_remote_exit = tempseat_notify_remote_exit,
diff --git a/windows/plink.c b/windows/plink.c
index 7506a13f..ef982be1 100644
--- a/windows/plink.c
+++ b/windows/plink.c
@@ -85,6 +85,7 @@ static const SeatVtable plink_seat_vt = {
     .output = plink_output,
     .eof = plink_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner_to_stderr,
     .get_userpass_input = plink_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = nullseat_notify_remote_exit,
diff --git a/windows/window.c b/windows/window.c
index 4c67009b..1aa83743 100644
--- a/windows/window.c
+++ b/windows/window.c
@@ -332,6 +332,7 @@ static const SeatVtable win_seat_vt = {
     .output = win_seat_output,
     .eof = win_seat_eof,
     .sent = nullseat_sent,
+    .banner = nullseat_banner_to_stderr,
     .get_userpass_input = win_seat_get_userpass_input,
     .notify_session_started = nullseat_notify_session_started,
     .notify_remote_exit = win_seat_notify_remote_exit,