diff --git a/cmd/server/observer_mail.go b/cmd/server/observer_mail.go
index baef4715..c51cf33f 100644
--- a/cmd/server/observer_mail.go
+++ b/cmd/server/observer_mail.go
@@ -75,8 +75,9 @@ func (a *authService) observerCredentialsMail(u *users.User, username, password
 
 // firmwareServer is the mqtt1.server value for the Dutch-MeshCore firmware.
 // For a bare host the firmware picks the scheme from the port alone (8883
-// mqtts, 443 wss, anything else mqtt), so the scheme is always given. The
-// firmware then appends mqtt1.port itself.
+// mqtts, 443 wss, anything else mqtt) and appends mqtt1.port itself. Firmware
+// before the merge 32dd8ad (2026-10-19) does not accept a scheme in the
+// server, so the host stays bare unless the port would pick the wrong scheme.
 func firmwareServer(o observerLoginSettings) string {
 	scheme := "mqtt"
 	if o.transport == "websockets" {
@@ -85,5 +86,15 @@ func firmwareServer(o observerLoginSettings) string {
 	if o.tls {
 		scheme += "s"
 	}
+	inferred := "mqtt"
+	switch o.port {
+	case 8883:
+		inferred = "mqtts"
+	case 443:
+		inferred = "wss"
+	}
+	if scheme == inferred {
+		return o.host
+	}
 	return scheme + "://" + o.host
 }
diff --git a/cmd/server/observer_mail_test.go b/cmd/server/observer_mail_test.go
index 72a9c280..44efd751 100644
--- a/cmd/server/observer_mail_test.go
+++ b/cmd/server/observer_mail_test.go
@@ -59,20 +59,29 @@ password = "p<w>"`
 // The firmware infers the scheme of a bare host from the port alone (8883
 // mqtts, 443 wss, else mqtt: MQTTBridge.cpp setupSlot), so the mail always
 // names the scheme the configured transport and TLS need.
+// Firmware before the Dutch-MeshCore merge 32dd8ad (2026-10-19) does not parse a
+// scheme in mqtt1.server and builds "<proto>://<host>:<port>" with proto taken
+// from the port alone (8883 mqtts, 443 wss, else mqtt). A bare host works on
+// both; the scheme is only written when the port would infer the wrong one.
 func TestFirmwareServerScheme(t *testing.T) {
 	for _, c := range []struct {
+		port      int
 		transport string
 		tls       bool
 		want      string
 	}{
-		{"tcp", false, "mqtt://mqtt.example.org"},
-		{"tcp", true, "mqtts://mqtt.example.org"},
-		{"websockets", false, "ws://mqtt.example.org"},
-		{"websockets", true, "wss://mqtt.example.org"},
+		{1883, "tcp", false, "mqtt.example.org"},
+		{8883, "tcp", true, "mqtt.example.org"},
+		{443, "websockets", true, "mqtt.example.org"},
+		{8884, "tcp", false, "mqtt.example.org"},
+		{8884, "tcp", true, "mqtts://mqtt.example.org"},
+		{8884, "websockets", false, "ws://mqtt.example.org"},
+		{8884, "websockets", true, "wss://mqtt.example.org"},
+		{8883, "tcp", false, "mqtt://mqtt.example.org"},
 	} {
-		o := observerLoginSettings{host: "mqtt.example.org", port: 8884, transport: c.transport, tls: c.tls}
+		o := observerLoginSettings{host: "mqtt.example.org", port: c.port, transport: c.transport, tls: c.tls}
 		if got := firmwareServer(o); got != c.want {
-			t.Errorf("%s tls=%v: got %q, want %q", c.transport, c.tls, got, c.want)
+			t.Errorf("port %d %s tls=%v: got %q, want %q", c.port, c.transport, c.tls, got, c.want)
 		}
 	}
 }
diff --git a/docs/observer-mqtt-logins.md b/docs/observer-mqtt-logins.md
index 594ccd59..4cb88c2c 100644
--- a/docs/observer-mqtt-logins.md
+++ b/docs/observer-mqtt-logins.md
@@ -68,9 +68,11 @@ reverse proxy for everything except the broker.
 
 The credentials mail holds the login in four forms: a meshcoretomqtt `[[broker]]` block, the
 Dutch-MeshCore observer firmware commands, a Home Assistant meshcore-ha block, and the plain values. For the firmware the server
-line always carries a scheme (`set mqtt1.server mqtts://mqtt.example.org`), because a bare host
-makes the firmware choose the scheme from the port alone (8883 TLS, 443 secure websockets,
-anything else plain MQTT).
+line is the bare host (`set mqtt1.server mqtt.example.org`): the firmware chooses the scheme
+from the port alone (8883 TLS, 443 secure websockets, anything else plain MQTT), and firmware
+before 2026-10-19 does not accept a scheme in the server. Only when the port would pick the
+wrong scheme (for example TLS on 8884) does the mail write one (`mqtts://mqtt.example.org`),
+which needs firmware from 2026-10-19 or later.
 
 Websockets: meshcoretomqtt connects with websocket path `/`, EMQX listens on `/mqtt` by
 default. Match the listener path to your uploaders, or use `tcp`.