diff --git a/src/header/sys_uio/cbindgen.toml b/src/header/sys_uio/cbindgen.toml
index 14fe43aeaa..c9e6d2aab1 100644
--- a/src/header/sys_uio/cbindgen.toml
+++ b/src/header/sys_uio/cbindgen.toml
@@ -8,6 +8,7 @@ after_includes = """
 #include <bits/ssize-t.h> // for ssize_t from sys/types.h
 #include <bits/iovec.h>   // for iovec
 
+// TODO should be guarded by _DEFAULT_SOURCE or _BSD_SOURCE
 // for Non-POSIX functions preadv and pwritev
 #include <bits/off-t.h>   // for off_t from sys/types.h
 """
diff --git a/src/header/sys_uio/mod.rs b/src/header/sys_uio/mod.rs
index fc52159a24..1c5e43473d 100644
--- a/src/header/sys_uio/mod.rs
+++ b/src/header/sys_uio/mod.rs
@@ -14,6 +14,7 @@ use crate::{
 
 pub use crate::header::bits_iovec::{gather, iovec, scatter};
 
+// TODO should be guarded by _DEFAULT_SOURCE or _BSD_SOURCE
 /// Non-POSIX, see <https://man7.org/linux/man-pages/man2/readv.2.html>.
 ///
 /// Combines the functionality of `readv()` and `pread()`.
@@ -42,6 +43,7 @@ pub unsafe extern "C" fn preadv(
     ret
 }
 
+// TODO should be guarded by _DEFAULT_SOURCE or _BSD_SOURCE
 /// Non-POSIX, see <https://man7.org/linux/man-pages/man2/readv.2.html>.
 ///
 /// Combined the functionality of `writev()` and `pwrite()`.