diff --git a/src/modules/module-rtp-sap.c b/src/modules/module-rtp-sap.c
index e49884d83..dbcadbbc0 100644
--- a/src/modules/module-rtp-sap.c
+++ b/src/modules/module-rtp-sap.c
@@ -740,6 +740,9 @@ static struct session *session_new_announce(struct impl *impl, struct node *node
 	if ((str = pw_properties_get(props, "rtp.ts-refclk")) != NULL)
 		sdp->ts_refclk = strdup(str);
 	if ((str = pw_properties_get(props, PW_KEY_NODE_CHANNELNAMES)) != NULL) {
+		struct spa_strbuf buf;
+		spa_strbuf_init(&buf, sdp->channelmap, sizeof(sdp->channelmap));
+
 		struct spa_json it[2];
 		char v[256];
 
@@ -748,10 +751,9 @@ static struct session *session_new_announce(struct impl *impl, struct node *node
 			spa_json_init(&it[1], str, strlen(str));
 
 		if (spa_json_get_string(&it[1], v, sizeof(v)) > 0)
-			snprintf(sdp->channelmap, sizeof(sdp->channelmap) - 1, "%s", v);
+			spa_strbuf_append(&buf, "%s", v);
 		while (spa_json_get_string(&it[1], v, sizeof(v)) > 0)
-			snprintf(sdp->channelmap + strlen(sdp->channelmap),
-				sizeof(sdp->channelmap) - strlen(sdp->channelmap) - 1, ", %s", v);
+			spa_strbuf_append(&buf, ", %s", v);
 	}
 
 	pw_log_info("created new session for node:%u", node->id);