diff --git a/spa/plugins/audioconvert/audioconvert.c b/spa/plugins/audioconvert/audioconvert.c
index 9477e3e75..285aa1903 100644
--- a/spa/plugins/audioconvert/audioconvert.c
+++ b/spa/plugins/audioconvert/audioconvert.c
@@ -287,6 +287,9 @@ static int setup_convert(struct impl *this)
 			outport->format.info.raw.rate,
 			outport->format.info.raw.layout);
 
+	if (this->n_links > 0)
+		return 0;
+
 	/* unpack */
 	make_link(this, NULL, 0, this->fmt_in, 0, &inport->format);
 	prev = this->fmt_in;
diff --git a/src/examples/video-play.c b/src/examples/video-play.c
index 96215a43c..918a078b5 100644
--- a/src/examples/video-play.c
+++ b/src/examples/video-play.c
@@ -100,6 +100,9 @@ on_process(void *_data)
 	uint8_t *src, *dst;
 
 	b = pw_stream_dequeue_buffer(stream);
+	if (b == NULL)
+		return;
+
 	buf = b->buffer;
 
 	pw_log_trace("new buffer %d", buf->id);
diff --git a/src/pipewire/link.c b/src/pipewire/link.c
index 7692e803e..9e540dd78 100644
--- a/src/pipewire/link.c
+++ b/src/pipewire/link.c
@@ -1198,6 +1198,10 @@ struct pw_link *pw_link_new(struct pw_core *core,
 	if (output == input)
 		goto same_ports;
 
+	if (output->direction != PW_DIRECTION_OUTPUT ||
+	    input->direction != PW_DIRECTION_INPUT)
+		goto wrong_direction;
+
 	if (pw_link_find(output, input))
 		goto link_exists;
 
@@ -1276,6 +1280,9 @@ struct pw_link *pw_link_new(struct pw_core *core,
       same_ports:
 	asprintf(error, "can't link the same ports");
 	return NULL;
+      wrong_direction:
+	asprintf(error, "ports have wrong direction");
+	return NULL;
       link_exists:
 	asprintf(error, "link already exists");
 	return NULL;
diff --git a/src/pipewire/node.c b/src/pipewire/node.c
index bbc833046..e66187a09 100644
--- a/src/pipewire/node.c
+++ b/src/pipewire/node.c
@@ -815,8 +815,10 @@ struct pw_port *pw_node_get_free_port(struct pw_node *node, enum pw_direction di
 
 	/* first try to find an unlinked port */
 	spa_list_for_each(p, ports, link) {
-		if (spa_list_is_empty(&p->links))
-			return p;
+		if (spa_list_is_empty(&p->links)) {
+			port = p;
+			goto found;
+		}
 		/* for output we can reuse an existing port, for input only
 		 * when there is a multiplex */
 		if (direction == PW_DIRECTION_OUTPUT || p->mix != NULL)
@@ -841,6 +843,7 @@ struct pw_port *pw_node_get_free_port(struct pw_node *node, enum pw_direction di
 	} else {
 		port = mixport;
 	}
+      found:
 	pw_log_debug("node %p: return port %p", node, port);
 	return port;