diff --git a/openbsc/include/openbsc/bsc_nat.h b/openbsc/include/openbsc/bsc_nat.h
index 682447a..280fa50 100644
--- a/openbsc/include/openbsc/bsc_nat.h
+++ b/openbsc/include/openbsc/bsc_nat.h
@@ -298,6 +298,7 @@
 
 int bsc_write(struct bsc_connection *bsc, struct msgb *msg, int id);
 int bsc_do_write(struct write_queue *queue, struct msgb *msg, int id);
+int bsc_write_cb(struct bsc_fd *bfd, struct msgb *msg);
 
 /* IMSI allow/deny handling */
 void bsc_parse_reg(void *ctx, regex_t *reg, char **imsi, int argc, const char **argv);