diff --git a/proxy/sshproxy.c b/proxy/sshproxy.c
index a26ccb04..49d1ea98 100644
--- a/proxy/sshproxy.c
+++ b/proxy/sshproxy.c
@@ -502,6 +502,7 @@ static const SeatVtable SshProxy_seat_vt = {
     .stripctrl_new = sshproxy_stripctrl_new,
     .set_trust_status = sshproxy_set_trust_status,
     .can_set_trust_status = sshproxy_can_set_trust_status,
+    .has_mixed_input_stream = nullseat_has_mixed_input_stream_no,
     .verbose = sshproxy_verbose,
     .interactive = sshproxy_interactive,
     .get_cursor_position = nullseat_get_cursor_position,
diff --git a/pscp.c b/pscp.c
index 13e89812..837e89d9 100644
--- a/pscp.c
+++ b/pscp.c
@@ -87,6 +87,7 @@ static const SeatVtable pscp_seat_vt = {
     .stripctrl_new = console_stripctrl_new,
     .set_trust_status = nullseat_set_trust_status,
     .can_set_trust_status = nullseat_can_set_trust_status_yes,
+    .has_mixed_input_stream = nullseat_has_mixed_input_stream_no,
     .verbose = cmdline_seat_verbose,
     .interactive = nullseat_interactive_no,
     .get_cursor_position = nullseat_get_cursor_position,
diff --git a/psftp.c b/psftp.c
index 14483569..d0317c2e 100644
--- a/psftp.c
+++ b/psftp.c
@@ -68,6 +68,7 @@ static const SeatVtable psftp_seat_vt = {
     .stripctrl_new = console_stripctrl_new,
     .set_trust_status = nullseat_set_trust_status,
     .can_set_trust_status = nullseat_can_set_trust_status_yes,
+    .has_mixed_input_stream = nullseat_has_mixed_input_stream_no,
     .verbose = cmdline_seat_verbose,
     .interactive = nullseat_interactive_yes,
     .get_cursor_position = nullseat_get_cursor_position,
diff --git a/putty.h b/putty.h
index 0047156f..232bbe30 100644
--- a/putty.h
+++ b/putty.h
@@ -1289,6 +1289,18 @@ struct SeatVtable {
      */
     bool (*can_set_trust_status)(Seat *seat);
 
+    /*
+     * Query whether this Seat's interactive prompt responses and its
+     * session input come from the same place.
+     *
+     * If false, this is used to suppress the final 'Press Return to
+     * begin session' anti-spoofing prompt in Plink. For example,
+     * Plink itself sets this flag if its standard input is redirected
+     * (and therefore not coming from the same place as the console
+     * it's sending its prompts to).
+     */
+    bool (*has_mixed_input_stream)(Seat *seat);
+
     /*
      * Ask the seat whether it would like verbose messages.
      */
@@ -1365,6 +1377,8 @@ static inline void seat_set_trust_status(Seat *seat, bool trusted)
 { seat->vt->set_trust_status(seat, trusted); }
 static inline bool seat_can_set_trust_status(Seat *seat)
 { return seat->vt->can_set_trust_status(seat); }
+static inline bool seat_has_mixed_input_stream(Seat *seat)
+{ return seat->vt->has_mixed_input_stream(seat); }
 static inline bool seat_verbose(Seat *seat)
 { return seat->vt->verbose(seat); }
 static inline bool seat_interactive(Seat *seat)
@@ -1437,6 +1451,8 @@ StripCtrlChars *nullseat_stripctrl_new(
 void nullseat_set_trust_status(Seat *seat, bool trusted);
 bool nullseat_can_set_trust_status_yes(Seat *seat);
 bool nullseat_can_set_trust_status_no(Seat *seat);
+bool nullseat_has_mixed_input_stream_yes(Seat *seat);
+bool nullseat_has_mixed_input_stream_no(Seat *seat);
 bool nullseat_verbose_no(Seat *seat);
 bool nullseat_verbose_yes(Seat *seat);
 bool nullseat_interactive_no(Seat *seat);
@@ -1463,6 +1479,7 @@ StripCtrlChars *console_stripctrl_new(
         Seat *seat, BinarySink *bs_out, SeatInteractionContext sic);
 void console_set_trust_status(Seat *seat, bool trusted);
 bool console_can_set_trust_status(Seat *seat);
+bool console_has_mixed_input_stream(Seat *seat);
 
 /*
  * Other centralised seat functions.
diff --git a/ssh/connection1-client.c b/ssh/connection1-client.c
index 7429b892..41bf9716 100644
--- a/ssh/connection1-client.c
+++ b/ssh/connection1-client.c
@@ -544,5 +544,9 @@ SshChannel *ssh1_serverside_agent_open(ConnectionLayer *cl, Channel *chan)
 bool ssh1_connection_need_antispoof_prompt(struct ssh1_connection_state *s)
 {
     seat_set_trust_status(s->ppl.seat, false);
-    return !seat_can_set_trust_status(s->ppl.seat);
+    if (!seat_has_mixed_input_stream(s->ppl.seat))
+        return false;
+    if (seat_can_set_trust_status(s->ppl.seat))
+        return false;
+    return true;
 }
diff --git a/ssh/connection2-client.c b/ssh/connection2-client.c
index 88338500..f17d1e21 100644
--- a/ssh/connection2-client.c
+++ b/ssh/connection2-client.c
@@ -501,6 +501,11 @@ void ssh2channel_send_terminal_size_change(SshChannel *sc, int w, int h)
 bool ssh2_connection_need_antispoof_prompt(struct ssh2_connection_state *s)
 {
     seat_set_trust_status(s->ppl.seat, false);
-    bool success = seat_can_set_trust_status(s->ppl.seat);
-    return (!success && !ssh_is_bare(s->ppl.ssh));
+    if (!seat_has_mixed_input_stream(s->ppl.seat))
+        return false;
+    if (seat_can_set_trust_status(s->ppl.seat))
+        return false;
+    if (ssh_is_bare(s->ppl.ssh))
+        return false;
+    return true;
 }
diff --git a/ssh/server.c b/ssh/server.c
index 99237616..347aa14b 100644
--- a/ssh/server.c
+++ b/ssh/server.c
@@ -128,6 +128,7 @@ static const SeatVtable server_seat_vt = {
     .stripctrl_new = nullseat_stripctrl_new,
     .set_trust_status = nullseat_set_trust_status,
     .can_set_trust_status = nullseat_can_set_trust_status_no,
+    .has_mixed_input_stream = nullseat_has_mixed_input_stream_no,
     .verbose = nullseat_verbose_no,
     .interactive = nullseat_interactive_no,
     .get_cursor_position = nullseat_get_cursor_position,
diff --git a/ssh/sesschan.c b/ssh/sesschan.c
index 5379b308..15b8bb4e 100644
--- a/ssh/sesschan.c
+++ b/ssh/sesschan.c
@@ -207,6 +207,7 @@ static const SeatVtable sesschan_seat_vt = {
     .stripctrl_new = nullseat_stripctrl_new,
     .set_trust_status = nullseat_set_trust_status,
     .can_set_trust_status = nullseat_can_set_trust_status_no,
+    .has_mixed_input_stream = nullseat_has_mixed_input_stream_no,
     .verbose = nullseat_verbose_no,
     .interactive = nullseat_interactive_no,
     .get_cursor_position = nullseat_get_cursor_position,
diff --git a/unix/console.c b/unix/console.c
index da795614..4131abdc 100644
--- a/unix/console.c
+++ b/unix/console.c
@@ -328,19 +328,11 @@ void console_set_trust_status(Seat *seat, bool trusted)
 
 bool console_can_set_trust_status(Seat *seat)
 {
-    if (console_batch_mode || !is_interactive() || !console_antispoof_prompt) {
+    if (console_batch_mode) {
         /*
          * In batch mode, we don't need to worry about the server
          * mimicking our interactive authentication, because the user
          * already knows not to expect any.
-         *
-         * If standard input isn't connected to a terminal, likewise,
-         * because even if the server did send a spoof authentication
-         * prompt, the user couldn't respond to it via the terminal
-         * anyway.
-         *
-         * We also return true without enabling any defences if the
-         * user has purposely disabled the antispoof prompt.
          */
         return true;
     }
@@ -348,6 +340,23 @@ bool console_can_set_trust_status(Seat *seat)
     return false;
 }
 
+bool console_has_mixed_input_stream(Seat *seat)
+{
+    if (!is_interactive() || !console_antispoof_prompt) {
+        /*
+         * If standard input isn't connected to a terminal, then even
+         * if the server did send a spoof authentication prompt, the
+         * user couldn't respond to it via the terminal anyway.
+         *
+         * We also pretend this is true if the user has purposely
+         * disabled the antispoof prompt.
+         */
+        return false;
+    }
+
+    return true;
+}
+
 /*
  * Warn about the obsolescent key file format.
  *
diff --git a/unix/plink.c b/unix/plink.c
index dee0cbec..446bef21 100644
--- a/unix/plink.c
+++ b/unix/plink.c
@@ -411,6 +411,7 @@ static const SeatVtable plink_seat_vt = {
     .stripctrl_new = console_stripctrl_new,
     .set_trust_status = console_set_trust_status,
     .can_set_trust_status = console_can_set_trust_status,
+    .has_mixed_input_stream = console_has_mixed_input_stream,
     .verbose = cmdline_seat_verbose,
     .interactive = plink_seat_interactive,
     .get_cursor_position = nullseat_get_cursor_position,
diff --git a/unix/window.c b/unix/window.c
index c5894ffa..c9d635ab 100644
--- a/unix/window.c
+++ b/unix/window.c
@@ -414,6 +414,7 @@ static const SeatVtable gtk_seat_vt = {
     .stripctrl_new = gtk_seat_stripctrl_new,
     .set_trust_status = gtk_seat_set_trust_status,
     .can_set_trust_status = gtk_seat_can_set_trust_status,
+    .has_mixed_input_stream = nullseat_has_mixed_input_stream_yes,
     .verbose = nullseat_verbose_yes,
     .interactive = nullseat_interactive_yes,
     .get_cursor_position = gtk_seat_get_cursor_position,
diff --git a/utils/nullseat.c b/utils/nullseat.c
index a53f563e..43a338fb 100644
--- a/utils/nullseat.c
+++ b/utils/nullseat.c
@@ -41,6 +41,8 @@ StripCtrlChars *nullseat_stripctrl_new(
 void nullseat_set_trust_status(Seat *seat, bool trusted) {}
 bool nullseat_can_set_trust_status_yes(Seat *seat) { return true; }
 bool nullseat_can_set_trust_status_no(Seat *seat) { return false; }
+bool nullseat_has_mixed_input_stream_yes(Seat *seat) { return true; }
+bool nullseat_has_mixed_input_stream_no(Seat *seat) { return false; }
 bool nullseat_verbose_no(Seat *seat) { return false; }
 bool nullseat_verbose_yes(Seat *seat) { return true; }
 bool nullseat_interactive_no(Seat *seat) { return false; }
diff --git a/utils/tempseat.c b/utils/tempseat.c
index eac10f8d..e1956eaa 100644
--- a/utils/tempseat.c
+++ b/utils/tempseat.c
@@ -198,6 +198,12 @@ static bool tempseat_can_set_trust_status(Seat *seat)
     return seat_can_set_trust_status(ts->realseat);
 }
 
+static bool tempseat_has_mixed_input_stream(Seat *seat)
+{
+    TempSeat *ts = container_of(seat, TempSeat, seat);
+    return seat_has_mixed_input_stream(ts->realseat);
+}
+
 /* ----------------------------------------------------------------------
  * Methods that should never be called on a TempSeat, so we can put an
  * unreachable() in them.
@@ -324,6 +330,7 @@ static const struct SeatVtable tempseat_vt = {
     .stripctrl_new = tempseat_stripctrl_new,
     .set_trust_status = tempseat_set_trust_status,
     .can_set_trust_status = tempseat_can_set_trust_status,
+    .has_mixed_input_stream = tempseat_has_mixed_input_stream,
     .verbose = tempseat_verbose,
     .interactive = tempseat_interactive,
     .get_cursor_position = tempseat_get_cursor_position,
diff --git a/windows/console.c b/windows/console.c
index abd31270..9fa9d7f0 100644
--- a/windows/console.c
+++ b/windows/console.c
@@ -194,19 +194,11 @@ void console_set_trust_status(Seat *seat, bool trusted)
 
 bool console_can_set_trust_status(Seat *seat)
 {
-    if (console_batch_mode || !is_interactive() || !console_antispoof_prompt) {
+    if (console_batch_mode) {
         /*
          * In batch mode, we don't need to worry about the server
          * mimicking our interactive authentication, because the user
          * already knows not to expect any.
-         *
-         * If standard input isn't connected to a terminal, likewise,
-         * because even if the server did send a spoof authentication
-         * prompt, the user couldn't respond to it via the terminal
-         * anyway.
-         *
-         * We also return true without enabling any defences if the
-         * user has purposely disabled the antispoof prompt.
          */
         return true;
     }
@@ -214,6 +206,23 @@ bool console_can_set_trust_status(Seat *seat)
     return false;
 }
 
+bool console_has_mixed_input_stream(Seat *seat)
+{
+    if (!is_interactive() || !console_antispoof_prompt) {
+        /*
+         * If standard input isn't connected to a terminal, then even
+         * if the server did send a spoof authentication prompt, the
+         * user couldn't respond to it via the terminal anyway.
+         *
+         * We also pretend this is true if the user has purposely
+         * disabled the antispoof prompt.
+         */
+        return false;
+    }
+
+    return true;
+}
+
 /*
  * Ask whether to wipe a session log file before writing to it.
  * Returns 2 for wipe, 1 for append, 0 for cancel (don't log).
diff --git a/windows/plink.c b/windows/plink.c
index ef982be1..8dc44c9e 100644
--- a/windows/plink.c
+++ b/windows/plink.c
@@ -105,6 +105,7 @@ static const SeatVtable plink_seat_vt = {
     .stripctrl_new = console_stripctrl_new,
     .set_trust_status = console_set_trust_status,
     .can_set_trust_status = console_can_set_trust_status,
+    .has_mixed_input_stream = console_has_mixed_input_stream,
     .verbose = cmdline_seat_verbose,
     .interactive = plink_seat_interactive,
     .get_cursor_position = nullseat_get_cursor_position,
diff --git a/windows/window.c b/windows/window.c
index 1aa83743..8ab371bb 100644
--- a/windows/window.c
+++ b/windows/window.c
@@ -352,6 +352,7 @@ static const SeatVtable win_seat_vt = {
     .stripctrl_new = win_seat_stripctrl_new,
     .set_trust_status = win_seat_set_trust_status,
     .can_set_trust_status = win_seat_can_set_trust_status,
+    .has_mixed_input_stream = nullseat_has_mixed_input_stream_yes,
     .verbose = nullseat_verbose_yes,
     .interactive = nullseat_interactive_yes,
     .get_cursor_position = win_seat_get_cursor_position,