diff --git a/src/librustc_data_structures/flock.rs b/src/librustc_data_structures/flock.rs
index 01f25a054f0a7949635a74a703080f0528c7a287..88b9ac5a4bd918e3d32d4ef95ea093a9626c948f 100644
--- a/src/librustc_data_structures/flock.rs
+++ b/src/librustc_data_structures/flock.rs
@@ -15,7 +15,7 @@
         use std::ffi::{CString, OsStr};
         use std::os::unix::prelude::*;
 
-        #[cfg(any(target_os = "linux", target_os = "android"))]
+        #[cfg(any(target_os = "linux", target_os = "android", target_os = "redox"))]
         mod os {
             #[repr(C)]
             pub struct flock {