diff --git a/arch/sim/src/sim/posix/vpnkit/sim_protocol.c b/arch/sim/src/sim/posix/vpnkit/sim_protocol.c
index 8567f046ee..23c408e446 100644
--- a/arch/sim/src/sim/posix/vpnkit/sim_protocol.c
+++ b/arch/sim/src/sim/posix/vpnkit/sim_protocol.c
@@ -150,7 +150,7 @@ err:
   return -1;
 }
 
-struct init_message *create_init_message()
+struct init_message *create_init_message(void)
 {
   struct init_message *m;