diff --git a/tests/fsm/fsm_test.c b/tests/fsm/fsm_test.c
index edbba9ef7..7a644213f 100644
--- a/tests/fsm/fsm_test.c
+++ b/tests/fsm/fsm_test.c
@@ -53,7 +53,7 @@ static void test_fsm_one(struct osmo_fsm_inst *fi, uint32_t event, void *data)
 	}
 }
 
-static void test_fsm_tmr_cb(struct osmo_fsm_inst *fi)
+static int test_fsm_tmr_cb(struct osmo_fsm_inst *fi)
 {
 	OSMO_ASSERT(fi->T == 2342);
 	OSMO_ASSERT(fi->state == ST_TWO);