diff --git a/spa/plugins/bluez5/backend-native.c b/spa/plugins/bluez5/backend-native.c
index ecea26d18..968387618 100644
--- a/spa/plugins/bluez5/backend-native.c
+++ b/spa/plugins/bluez5/backend-native.c
@@ -1733,8 +1733,8 @@ static void sco_event(struct spa_source *source)
 		}
 	}
 
-	if (source->rmask & SPA_IO_IN) {
-		SPA_FLAG_UPDATE(source->mask, SPA_IO_IN, false);
+	if (source->rmask & (SPA_IO_OUT | SPA_IO_IN)) {
+		SPA_FLAG_CLEAR(source->mask, SPA_IO_OUT | SPA_IO_IN);
 		spa_loop_update_source(backend->main_loop, source);
 		sco_ready(t);
 	}
@@ -1750,15 +1750,25 @@ static void sco_start_source(struct spa_bt_transport *t)
 
 	td->err = -EINPROGRESS;
 
-	/*
-	 * We on purpose wait for POLLIN when connecting (not POLLOUT as usual), to
-	 * indicate ready only after we are sure the device is sending data.
-	 */
 	td->sco.func = sco_event;
 	td->sco.data = t;
 	td->sco.fd = t->fd;
-	td->sco.mask = SPA_IO_HUP | SPA_IO_ERR | SPA_IO_IN;
+	td->sco.mask = SPA_IO_HUP | SPA_IO_ERR;
 	td->sco.rmask = 0;
+
+	switch (t->device->adapter->bus_type) {
+	case BUS_TYPE_USB:
+		/* With USB controllers, we have to determine packet size from incoming
+		 * packets before we can send. Wait for POLLIN when connecting (not
+		 * POLLOUT as usual).
+		 */
+		td->sco.mask |= SPA_IO_IN;
+		break;
+	default:
+		td->sco.mask |= SPA_IO_OUT;
+		break;
+	}
+
 	spa_loop_add_source(backend->main_loop, &td->sco);
 }
 
diff --git a/spa/plugins/bluez5/bluez5-dbus.c b/spa/plugins/bluez5/bluez5-dbus.c
index 47dabfeb8..63df1ff4c 100644
--- a/spa/plugins/bluez5/bluez5-dbus.c
+++ b/spa/plugins/bluez5/bluez5-dbus.c
@@ -3219,10 +3219,7 @@ static int spa_bt_transport_stop_volume_timer(struct spa_bt_transport *transport
 int spa_bt_transport_ensure_sco_io(struct spa_bt_transport *t, struct spa_loop *data_loop)
 {
 	if (t->sco_io == NULL) {
-		t->sco_io = spa_bt_sco_io_create(data_loop,
-						 t->fd,
-						 t->read_mtu,
-						 t->write_mtu);
+		t->sco_io = spa_bt_sco_io_create(t, data_loop, t->monitor->log);
 		if (t->sco_io == NULL)
 			return -ENOMEM;
 	}
diff --git a/spa/plugins/bluez5/defs.h b/spa/plugins/bluez5/defs.h
index a797073ec..ba9e54aca 100644
--- a/spa/plugins/bluez5/defs.h
+++ b/spa/plugins/bluez5/defs.h
@@ -571,7 +571,7 @@ struct spa_bt_iso_io;
 
 struct spa_bt_sco_io;
 
-struct spa_bt_sco_io *spa_bt_sco_io_create(struct spa_loop *data_loop, int fd, uint16_t read_mtu, uint16_t write_mtu);
+struct spa_bt_sco_io *spa_bt_sco_io_create(struct spa_bt_transport *transport, struct spa_loop *data_loop, struct spa_log *log);
 void spa_bt_sco_io_destroy(struct spa_bt_sco_io *io);
 void spa_bt_sco_io_set_source_cb(struct spa_bt_sco_io *io, int (*source_cb)(void *userdata, uint8_t *data, int size), void *userdata);
 void spa_bt_sco_io_set_sink_cb(struct spa_bt_sco_io *io, int (*sink_cb)(void *userdata), void *userdata);
diff --git a/spa/plugins/bluez5/sco-io.c b/spa/plugins/bluez5/sco-io.c
index cb72953d8..4b4b8f96d 100644
--- a/spa/plugins/bluez5/sco-io.c
+++ b/spa/plugins/bluez5/sco-io.c
@@ -30,6 +30,10 @@
 
 #include "defs.h"
 
+SPA_LOG_TOPIC_DEFINE_STATIC(log_topic, "spa.bluez5.sco-io");
+#undef SPA_LOG_TOPIC_DEFAULT
+#define SPA_LOG_TOPIC_DEFAULT &log_topic
+
 
 /* We'll use the read rx data size to find the correct packet size for writing,
  * since kernel might not report it as the socket MTU, see
@@ -54,6 +58,7 @@ struct spa_bt_sco_io {
 	uint16_t read_mtu;
 	uint16_t write_mtu;
 
+	struct spa_log *log;
 	struct spa_loop *data_loop;
 	struct spa_source source;
 
@@ -103,6 +108,9 @@ static void sco_io_on_ready(struct spa_source *source)
 			goto stop;
 		}
 
+		if (res != (int)io->read_size)
+			spa_log_trace(io->log, "%p: packet size:%d", io, res);
+
 		io->read_size = res;
 
 		if (io->source_cb) {
@@ -185,23 +193,42 @@ int spa_bt_sco_io_write(struct spa_bt_sco_io *io, uint8_t *buf, int size)
 }
 
 
-struct spa_bt_sco_io *spa_bt_sco_io_create(struct spa_loop *data_loop,
-                                           int fd,
-                                           uint16_t read_mtu,
-                                           uint16_t write_mtu)
+struct spa_bt_sco_io *spa_bt_sco_io_create(struct spa_bt_transport *transport, struct spa_loop *data_loop, struct spa_log *log)
 {
 	struct spa_bt_sco_io *io;
 
+	spa_log_topic_init(log, &log_topic);
+
 	io = calloc(1, sizeof(struct spa_bt_sco_io));
 	if (io == NULL)
 		return io;
 
-	io->fd = fd;
-	io->read_mtu = read_mtu;
-	io->write_mtu = write_mtu;
+	io->fd = transport->fd;
+	io->read_mtu = transport->read_mtu;
+	io->write_mtu = transport->write_mtu;
 	io->data_loop = data_loop;
+	io->log = log;
 
-	io->read_size = 0;
+	if (transport->device->adapter->bus_type == BUS_TYPE_USB) {
+		/* For USB we need to wait for RX to know it. Using wrong size doesn't
+		 * work anyway, and may result to errors printed to dmesg if too big.
+		 */
+		io->read_size = 0;
+	} else {
+		/* Set some sensible initial packet size */
+		switch (transport->codec) {
+		case HFP_AUDIO_CODEC_CVSD:
+			io->read_size = 48;  /* 3ms S16_LE 8000 Hz */
+			break;
+		case HFP_AUDIO_CODEC_MSBC:
+		case HFP_AUDIO_CODEC_LC3_SWB:
+		default:
+			io->read_size = HFP_CODEC_PACKET_SIZE;
+			break;
+		}
+	}
+
+	spa_log_debug(io->log, "%p: initial packet size:%d", io, io->read_size);
 
 	/* Add the ready callback */
 	io->source.data = io;