diff --git a/artiq/firmware/libdyld/lib.rs b/artiq/firmware/libdyld/lib.rs
index 1eeff2bf4..d16dc1cdd 100644
--- a/artiq/firmware/libdyld/lib.rs
+++ b/artiq/firmware/libdyld/lib.rs
@@ -1,5 +1,4 @@
 #![no_std]
-#![feature(untagged_unions)]
 
 use core::{mem, ptr, fmt, slice, str, convert};
 use elf::*;