diff --git a/src/client/main_fsm.c b/src/client/main_fsm.c
index 0674f6c..673b19e 100644
--- a/src/client/main_fsm.c
+++ b/src/client/main_fsm.c
@@ -75,9 +75,9 @@
 	env[i++] = talloc_asprintf(env, "REMSIM_CAUSE=%s", cause);
 
 	/* ask frontend to append any frontend-speccific additional environment vars */
-	rc = frontend_append_script_env(bc, env+i, 256-i);
+	rc = frontend_append_script_env(bc, env, i, 256-i-1);
 	if (rc > 0)
-		i += rc;
+		i = rc;
 
 	/* terminate last entry */
 	env[i++] = NULL;