diff --git a/src/tdef.c b/src/tdef.c
index 897a92f..9890f95 100644
--- a/src/tdef.c
+++ b/src/tdef.c
@@ -331,7 +331,7 @@
  */
 int _osmo_tdef_fsm_inst_state_chg(struct osmo_fsm_inst *fi, uint32_t state,
 				  const struct osmo_tdef_state_timeout *timeouts_array,
-				  const struct osmo_tdef *tdefs, unsigned long default_timeout,
+				  const struct osmo_tdef *tdefs, long default_timeout,
 				  const char *file, int line)
 {
 	const struct osmo_tdef_state_timeout *t = osmo_tdef_get_state_timeout(state, timeouts_array);