diff --git a/src/flag.rs b/src/flag.rs
index a8f22e63e8..fff6d17952 100644
--- a/src/flag.rs
+++ b/src/flag.rs
@@ -56,6 +56,9 @@ pub const F_SETFD: usize = 2;
 pub const F_GETFL: usize = 3;
 pub const F_SETFL: usize = 4;
 
+/// Duplicate file descriptor with close-on-exec set (Red Bear extension; libredox ABI).
+pub const F_DUPFD_CLOEXEC: usize = 5;
+
 pub const FUTEX_WAIT: usize = 0;
 pub const FUTEX_WAKE: usize = 1;
 pub const FUTEX_REQUEUE: usize = 2;
@@ -201,6 +204,9 @@ pub const O_NOFOLLOW: usize = 0x8000_0000;
 pub const O_ACCMODE: usize = O_RDONLY | O_WRONLY | O_RDWR;
 pub const O_FCNTL_MASK: usize = O_NONBLOCK | O_APPEND | O_ASYNC | O_FSYNC;
 
+/// Atomically set close-on-exec when opening a file (Red Bear extension; libredox ABI).
+pub const O_CLOEXEC: usize = 0x0100_0000;
+
 /// Remove directory instead of unlinking file.
 pub const AT_REMOVEDIR: usize = 0x200;