diff --git a/codex-rs/linux-sandbox/src/fd_cleanup.rs b/codex-rs/linux-sandbox/src/fd_cleanup.rs
index 8a82555501..3908f9f8fb 100644
--- a/codex-rs/linux-sandbox/src/fd_cleanup.rs
+++ b/codex-rs/linux-sandbox/src/fd_cleanup.rs
@@ -1,14 +1,15 @@
 //! File descriptor hygiene before entering the sandboxed command.
 
-/// Close helper-inherited descriptors that are not standard input/output/error.
+/// Mark helper-inherited descriptors close-on-exec unless they are standard
+/// input/output/error.
 ///
 /// The sandboxed command can still create allowed local IPC after exec, but it
 /// must not inherit an already-connected network socket from the launcher.
-pub(crate) fn close_inherited_fds() {
-    match close_fds_with_close_range() {
+pub(crate) fn mark_inherited_fds_cloexec() {
+    match set_cloexec_with_close_range() {
         Ok(()) => return,
         Err(err) if can_fallback_from_close_range(&err) => {}
-        Err(err) => panic!("failed to close inherited file descriptors: {err}"),
+        Err(err) => panic!("failed to mark inherited file descriptors close-on-exec: {err}"),
     }
 
     let fds = match non_stdio_fds_from_proc() {
@@ -16,17 +17,17 @@ pub(crate) fn close_inherited_fds() {
         Err(err) => panic!("failed to enumerate inherited file descriptors: {err}"),
     };
     for fd in fds {
-        close_fd_ignoring_badf(fd);
+        set_fd_cloexec_ignoring_badf(fd);
     }
 }
 
-fn close_fds_with_close_range() -> std::io::Result<()> {
+fn set_cloexec_with_close_range() -> std::io::Result<()> {
     let result = unsafe {
         libc::syscall(
             libc::SYS_close_range,
             (libc::STDERR_FILENO + 1) as libc::c_uint,
             u32::MAX as libc::c_uint,
-            0 as libc::c_uint,
+            libc::CLOSE_RANGE_CLOEXEC,
         )
     };
     if result == 0 {
@@ -39,7 +40,7 @@ fn close_fds_with_close_range() -> std::io::Result<()> {
 fn can_fallback_from_close_range(err: &std::io::Error) -> bool {
     matches!(
         err.raw_os_error(),
-        Some(code) if code == libc::ENOSYS || code == libc::EPERM
+        Some(code) if code == libc::ENOSYS || code == libc::EPERM || code == libc::EINVAL
     )
 }
 
@@ -61,13 +62,21 @@ fn non_stdio_fds_from_proc() -> std::io::Result<Vec<libc::c_int>> {
     Ok(fds)
 }
 
-fn close_fd_ignoring_badf(fd: libc::c_int) {
-    let result = unsafe { libc::close(fd) };
-    if result == 0 {
+fn set_fd_cloexec_ignoring_badf(fd: libc::c_int) {
+    let flags = unsafe { libc::fcntl(fd, libc::F_GETFD) };
+    if flags == -1 {
+        let err = std::io::Error::last_os_error();
+        if err.raw_os_error() != Some(libc::EBADF) {
+            panic!("failed to inspect inherited file descriptor {fd}: {err}");
+        }
         return;
     }
-    let err = std::io::Error::last_os_error();
-    if err.raw_os_error() != Some(libc::EBADF) {
-        panic!("failed to close inherited file descriptor {fd}: {err}");
+
+    let result = unsafe { libc::fcntl(fd, libc::F_SETFD, flags | libc::FD_CLOEXEC) };
+    if result == -1 {
+        let err = std::io::Error::last_os_error();
+        if err.raw_os_error() != Some(libc::EBADF) {
+            panic!("failed to mark inherited file descriptor {fd} close-on-exec: {err}");
+        }
     }
 }
diff --git a/codex-rs/linux-sandbox/src/linux_run_main.rs b/codex-rs/linux-sandbox/src/linux_run_main.rs
index 119f3fd9fc..605aa3601b 100644
--- a/codex-rs/linux-sandbox/src/linux_run_main.rs
+++ b/codex-rs/linux-sandbox/src/linux_run_main.rs
@@ -10,7 +10,7 @@ use std::path::PathBuf;
 use crate::bwrap::BwrapNetworkMode;
 use crate::bwrap::BwrapOptions;
 use crate::bwrap::create_bwrap_command_args;
-use crate::fd_cleanup::close_inherited_fds;
+use crate::fd_cleanup::mark_inherited_fds_cloexec;
 use crate::landlock::apply_sandbox_policy_to_current_thread;
 use crate::launcher::exec_bwrap;
 use crate::launcher::preferred_bwrap_supports_argv0;
@@ -730,7 +730,7 @@ fn exec_or_panic(command: Vec<String>) -> ! {
     let mut c_args_ptrs: Vec<*const libc::c_char> = c_args.iter().map(|arg| arg.as_ptr()).collect();
     c_args_ptrs.push(std::ptr::null());
 
-    close_inherited_fds();
+    mark_inherited_fds_cloexec();
 
     unsafe {
         libc::execvp(c_command.as_ptr(), c_args_ptrs.as_ptr());