diff --git a/test/unit/tcp/tcp_helper.c b/test/unit/tcp/tcp_helper.c
index 4a28b869..0957cbe4 100644
--- a/test/unit/tcp/tcp_helper.c
+++ b/test/unit/tcp/tcp_helper.c
@@ -121,6 +121,8 @@ tcp_set_state(struct tcp_pcb* pcb, enum tcp_state state, struct ip_addr* local_i
     pcb->local_port = local_port;
     pcb->remote_ip.addr = remote_ip->addr;
     pcb->remote_port = remote_port;
+  } else {
+    fail();
   }
 }