diff --git a/tools/hwsim.c b/tools/hwsim.c
index c28144c6..22799fc9 100644
--- a/tools/hwsim.c
+++ b/tools/hwsim.c
@@ -2090,7 +2090,7 @@ static void hwsim_ready(void *user_data)
 			msg_size += 4;
 
 		if (radio_name_attr)
-			msg_size += strlen(radio_name_attr) + 1;
+			msg_size += strlen(radio_name_attr) + 8;
 
 		if (no_vif_attr)
 			msg_size += 4;