diff --git a/library/std/src/os/wasi/io.rs b/library/std/src/os/wasi/io.rs
index cf4501b98cbd4..b6bc74da8e7b5 100644
--- a/library/std/src/os/wasi/io.rs
+++ b/library/std/src/os/wasi/io.rs
@@ -6,11 +6,18 @@
 use crate::fs;
 use crate::io;
 use crate::net;
+use crate::os::raw;
 use crate::sys;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
 
 /// Raw file descriptors.
-pub type RawFd = u32;
+///
+/// This has type `c_int` to ease compatibility with code that also compiles on
+/// Unix configurations, however unlike Unix and POSIX, in WASI negative file
+/// descriptors are valid. Only `-1` is reserved for indicating errors. Code
+/// intending to be portable across Unix platforms and WASI should avoid
+/// assuming that negative file descriptors are invalid.
+pub type RawFd = raw::c_int;
 
 /// A trait to extract the raw WASI file descriptor from an underlying
 /// object.
@@ -161,41 +168,41 @@ impl IntoRawFd for fs::File {
 impl AsRawFd for io::Stdin {
     #[inline]
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDIN_FILENO as RawFd
+        libc::STDIN_FILENO
     }
 }
 
 impl AsRawFd for io::Stdout {
     #[inline]
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDOUT_FILENO as RawFd
+        libc::STDOUT_FILENO
     }
 }
 
 impl AsRawFd for io::Stderr {
     #[inline]
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDERR_FILENO as RawFd
+        libc::STDERR_FILENO
     }
 }
 
 impl<'a> AsRawFd for io::StdinLock<'a> {
     #[inline]
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDIN_FILENO as RawFd
+        libc::STDIN_FILENO
     }
 }
 
 impl<'a> AsRawFd for io::StdoutLock<'a> {
     #[inline]
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDOUT_FILENO as RawFd
+        libc::STDOUT_FILENO
     }
 }
 
 impl<'a> AsRawFd for io::StderrLock<'a> {
     #[inline]
     fn as_raw_fd(&self) -> RawFd {
-        libc::STDERR_FILENO as RawFd
+        libc::STDERR_FILENO
     }
 }
diff --git a/library/std/src/sys/wasi/fd.rs b/library/std/src/sys/wasi/fd.rs
index ba66eba2ad38b..1f6ea8d6e8df3 100644
--- a/library/std/src/sys/wasi/fd.rs
+++ b/library/std/src/sys/wasi/fd.rs
@@ -5,10 +5,11 @@ use super::err2io;
 use crate::io::{self, IoSlice, IoSliceMut, SeekFrom};
 use crate::mem;
 use crate::net::Shutdown;
+use crate::os::raw::c_int;
 
 #[derive(Debug)]
 pub struct WasiFd {
-    fd: wasi::Fd,
+    fd: c_int,
 }
 
 fn iovec<'a>(a: &'a mut [IoSliceMut<'_>]) -> &'a [wasi::Iovec] {
@@ -26,38 +27,38 @@ fn ciovec<'a>(a: &'a [IoSlice<'_>]) -> &'a [wasi::Ciovec] {
 }
 
 impl WasiFd {
-    pub unsafe fn from_raw(fd: wasi::Fd) -> WasiFd {
+    pub unsafe fn from_raw(fd: c_int) -> WasiFd {
         WasiFd { fd }
     }
 
-    pub fn into_raw(self) -> wasi::Fd {
+    pub fn into_raw(self) -> c_int {
         let ret = self.fd;
         mem::forget(self);
         ret
     }
 
-    pub fn as_raw(&self) -> wasi::Fd {
+    pub fn as_raw(&self) -> c_int {
         self.fd
     }
 
     pub fn datasync(&self) -> io::Result<()> {
-        unsafe { wasi::fd_datasync(self.fd).map_err(err2io) }
+        unsafe { wasi::fd_datasync(self.fd as wasi::Fd).map_err(err2io) }
     }
 
     pub fn pread(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
-        unsafe { wasi::fd_pread(self.fd, iovec(bufs), offset).map_err(err2io) }
+        unsafe { wasi::fd_pread(self.fd as wasi::Fd, iovec(bufs), offset).map_err(err2io) }
     }
 
     pub fn pwrite(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
-        unsafe { wasi::fd_pwrite(self.fd, ciovec(bufs), offset).map_err(err2io) }
+        unsafe { wasi::fd_pwrite(self.fd as wasi::Fd, ciovec(bufs), offset).map_err(err2io) }
     }
 
     pub fn read(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
-        unsafe { wasi::fd_read(self.fd, iovec(bufs)).map_err(err2io) }
+        unsafe { wasi::fd_read(self.fd as wasi::Fd, iovec(bufs)).map_err(err2io) }
     }
 
     pub fn write(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
-        unsafe { wasi::fd_write(self.fd, ciovec(bufs)).map_err(err2io) }
+        unsafe { wasi::fd_write(self.fd as wasi::Fd, ciovec(bufs)).map_err(err2io) }
     }
 
     pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
@@ -66,37 +67,37 @@ impl WasiFd {
             SeekFrom::End(pos) => (wasi::WHENCE_END, pos),
             SeekFrom::Current(pos) => (wasi::WHENCE_CUR, pos),
         };
-        unsafe { wasi::fd_seek(self.fd, offset, whence).map_err(err2io) }
+        unsafe { wasi::fd_seek(self.fd as wasi::Fd, offset, whence).map_err(err2io) }
     }
 
     pub fn tell(&self) -> io::Result<u64> {
-        unsafe { wasi::fd_tell(self.fd).map_err(err2io) }
+        unsafe { wasi::fd_tell(self.fd as wasi::Fd).map_err(err2io) }
     }
 
     // FIXME: __wasi_fd_fdstat_get
 
     pub fn set_flags(&self, flags: wasi::Fdflags) -> io::Result<()> {
-        unsafe { wasi::fd_fdstat_set_flags(self.fd, flags).map_err(err2io) }
+        unsafe { wasi::fd_fdstat_set_flags(self.fd as wasi::Fd, flags).map_err(err2io) }
     }
 
     pub fn set_rights(&self, base: wasi::Rights, inheriting: wasi::Rights) -> io::Result<()> {
-        unsafe { wasi::fd_fdstat_set_rights(self.fd, base, inheriting).map_err(err2io) }
+        unsafe { wasi::fd_fdstat_set_rights(self.fd as wasi::Fd, base, inheriting).map_err(err2io) }
     }
 
     pub fn sync(&self) -> io::Result<()> {
-        unsafe { wasi::fd_sync(self.fd).map_err(err2io) }
+        unsafe { wasi::fd_sync(self.fd as wasi::Fd).map_err(err2io) }
     }
 
     pub fn advise(&self, offset: u64, len: u64, advice: wasi::Advice) -> io::Result<()> {
-        unsafe { wasi::fd_advise(self.fd, offset, len, advice).map_err(err2io) }
+        unsafe { wasi::fd_advise(self.fd as wasi::Fd, offset, len, advice).map_err(err2io) }
     }
 
     pub fn allocate(&self, offset: u64, len: u64) -> io::Result<()> {
-        unsafe { wasi::fd_allocate(self.fd, offset, len).map_err(err2io) }
+        unsafe { wasi::fd_allocate(self.fd as wasi::Fd, offset, len).map_err(err2io) }
     }
 
     pub fn create_directory(&self, path: &str) -> io::Result<()> {
-        unsafe { wasi::path_create_directory(self.fd, path).map_err(err2io) }
+        unsafe { wasi::path_create_directory(self.fd as wasi::Fd, path).map_err(err2io) }
     }
 
     pub fn link(
@@ -107,7 +108,14 @@ impl WasiFd {
         new_path: &str,
     ) -> io::Result<()> {
         unsafe {
-            wasi::path_link(self.fd, old_flags, old_path, new_fd.fd, new_path).map_err(err2io)
+            wasi::path_link(
+                self.fd as wasi::Fd,
+                old_flags,
+                old_path,
+                new_fd.fd as wasi::Fd,
+                new_path,
+            )
+            .map_err(err2io)
         }
     }
 
@@ -122,7 +130,7 @@ impl WasiFd {
     ) -> io::Result<WasiFd> {
         unsafe {
             wasi::path_open(
-                self.fd,
+                self.fd as wasi::Fd,
                 dirflags,
                 path,
                 oflags,
@@ -130,25 +138,34 @@ impl WasiFd {
                 fs_rights_inheriting,
                 fs_flags,
             )
-            .map(|fd| WasiFd::from_raw(fd))
+            .map(|fd| WasiFd::from_raw(fd as c_int))
             .map_err(err2io)
         }
     }
 
     pub fn readdir(&self, buf: &mut [u8], cookie: wasi::Dircookie) -> io::Result<usize> {
-        unsafe { wasi::fd_readdir(self.fd, buf.as_mut_ptr(), buf.len(), cookie).map_err(err2io) }
+        unsafe {
+            wasi::fd_readdir(self.fd as wasi::Fd, buf.as_mut_ptr(), buf.len(), cookie)
+                .map_err(err2io)
+        }
     }
 
     pub fn readlink(&self, path: &str, buf: &mut [u8]) -> io::Result<usize> {
-        unsafe { wasi::path_readlink(self.fd, path, buf.as_mut_ptr(), buf.len()).map_err(err2io) }
+        unsafe {
+            wasi::path_readlink(self.fd as wasi::Fd, path, buf.as_mut_ptr(), buf.len())
+                .map_err(err2io)
+        }
     }
 
     pub fn rename(&self, old_path: &str, new_fd: &WasiFd, new_path: &str) -> io::Result<()> {
-        unsafe { wasi::path_rename(self.fd, old_path, new_fd.fd, new_path).map_err(err2io) }
+        unsafe {
+            wasi::path_rename(self.fd as wasi::Fd, old_path, new_fd.fd as wasi::Fd, new_path)
+                .map_err(err2io)
+        }
     }
 
     pub fn filestat_get(&self) -> io::Result<wasi::Filestat> {
-        unsafe { wasi::fd_filestat_get(self.fd).map_err(err2io) }
+        unsafe { wasi::fd_filestat_get(self.fd as wasi::Fd).map_err(err2io) }
     }
 
     pub fn filestat_set_times(
@@ -157,11 +174,13 @@ impl WasiFd {
         mtim: wasi::Timestamp,
         fstflags: wasi::Fstflags,
     ) -> io::Result<()> {
-        unsafe { wasi::fd_filestat_set_times(self.fd, atim, mtim, fstflags).map_err(err2io) }
+        unsafe {
+            wasi::fd_filestat_set_times(self.fd as wasi::Fd, atim, mtim, fstflags).map_err(err2io)
+        }
     }
 
     pub fn filestat_set_size(&self, size: u64) -> io::Result<()> {
-        unsafe { wasi::fd_filestat_set_size(self.fd, size).map_err(err2io) }
+        unsafe { wasi::fd_filestat_set_size(self.fd as wasi::Fd, size).map_err(err2io) }
     }
 
     pub fn path_filestat_get(
@@ -169,7 +188,7 @@ impl WasiFd {
         flags: wasi::Lookupflags,
         path: &str,
     ) -> io::Result<wasi::Filestat> {
-        unsafe { wasi::path_filestat_get(self.fd, flags, path).map_err(err2io) }
+        unsafe { wasi::path_filestat_get(self.fd as wasi::Fd, flags, path).map_err(err2io) }
     }
 
     pub fn path_filestat_set_times(
@@ -181,21 +200,21 @@ impl WasiFd {
         fstflags: wasi::Fstflags,
     ) -> io::Result<()> {
         unsafe {
-            wasi::path_filestat_set_times(self.fd, flags, path, atim, mtim, fstflags)
+            wasi::path_filestat_set_times(self.fd as wasi::Fd, flags, path, atim, mtim, fstflags)
                 .map_err(err2io)
         }
     }
 
     pub fn symlink(&self, old_path: &str, new_path: &str) -> io::Result<()> {
-        unsafe { wasi::path_symlink(old_path, self.fd, new_path).map_err(err2io) }
+        unsafe { wasi::path_symlink(old_path, self.fd as wasi::Fd, new_path).map_err(err2io) }
     }
 
     pub fn unlink_file(&self, path: &str) -> io::Result<()> {
-        unsafe { wasi::path_unlink_file(self.fd, path).map_err(err2io) }
+        unsafe { wasi::path_unlink_file(self.fd as wasi::Fd, path).map_err(err2io) }
     }
 
     pub fn remove_directory(&self, path: &str) -> io::Result<()> {
-        unsafe { wasi::path_remove_directory(self.fd, path).map_err(err2io) }
+        unsafe { wasi::path_remove_directory(self.fd as wasi::Fd, path).map_err(err2io) }
     }
 
     pub fn sock_recv(
@@ -203,11 +222,11 @@ impl WasiFd {
         ri_data: &mut [IoSliceMut<'_>],
         ri_flags: wasi::Riflags,
     ) -> io::Result<(usize, wasi::Roflags)> {
-        unsafe { wasi::sock_recv(self.fd, iovec(ri_data), ri_flags).map_err(err2io) }
+        unsafe { wasi::sock_recv(self.fd as wasi::Fd, iovec(ri_data), ri_flags).map_err(err2io) }
     }
 
     pub fn sock_send(&self, si_data: &[IoSlice<'_>], si_flags: wasi::Siflags) -> io::Result<usize> {
-        unsafe { wasi::sock_send(self.fd, ciovec(si_data), si_flags).map_err(err2io) }
+        unsafe { wasi::sock_send(self.fd as wasi::Fd, ciovec(si_data), si_flags).map_err(err2io) }
     }
 
     pub fn sock_shutdown(&self, how: Shutdown) -> io::Result<()> {
@@ -216,7 +235,7 @@ impl WasiFd {
             Shutdown::Write => wasi::SDFLAGS_WR,
             Shutdown::Both => wasi::SDFLAGS_WR | wasi::SDFLAGS_RD,
         };
-        unsafe { wasi::sock_shutdown(self.fd, how).map_err(err2io) }
+        unsafe { wasi::sock_shutdown(self.fd as wasi::Fd, how).map_err(err2io) }
     }
 }
 
@@ -224,6 +243,6 @@ impl Drop for WasiFd {
     fn drop(&mut self) {
         // FIXME: can we handle the return code here even though we can't on
         // unix?
-        let _ = unsafe { wasi::fd_close(self.fd) };
+        let _ = unsafe { wasi::fd_close(self.fd as wasi::Fd) };
     }
 }
diff --git a/library/std/src/sys/wasi/fs.rs b/library/std/src/sys/wasi/fs.rs
index 8ffa1c88d88e7..55c9c652a8bbb 100644
--- a/library/std/src/sys/wasi/fs.rs
+++ b/library/std/src/sys/wasi/fs.rs
@@ -6,6 +6,7 @@ use crate::fmt;
 use crate::io::{self, IoSlice, IoSliceMut, SeekFrom};
 use crate::iter;
 use crate::mem::{self, ManuallyDrop};
+use crate::os::raw::c_int;
 use crate::os::wasi::ffi::{OsStrExt, OsStringExt};
 use crate::path::{Path, PathBuf};
 use crate::ptr;
@@ -454,8 +455,8 @@ impl File {
     }
 }
 
-impl FromInner<u32> for File {
-    fn from_inner(fd: u32) -> File {
+impl FromInner<c_int> for File {
+    fn from_inner(fd: c_int) -> File {
         unsafe { File { fd: WasiFd::from_raw(fd) } }
     }
 }
@@ -653,7 +654,7 @@ fn open_parent(p: &Path) -> io::Result<(ManuallyDrop<WasiFd>, PathBuf)> {
             let relative = CStr::from_ptr(relative_path).to_bytes().to_vec();
 
             return Ok((
-                ManuallyDrop::new(WasiFd::from_raw(fd as u32)),
+                ManuallyDrop::new(WasiFd::from_raw(fd as c_int)),
                 PathBuf::from(OsString::from_vec(relative)),
             ));
         }
diff --git a/library/std/src/sys/wasi/net.rs b/library/std/src/sys/wasi/net.rs
index 06860673d90e0..50b7352933e57 100644
--- a/library/std/src/sys/wasi/net.rs
+++ b/library/std/src/sys/wasi/net.rs
@@ -5,6 +5,7 @@ use crate::convert::TryFrom;
 use crate::fmt;
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::net::{Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr};
+use crate::os::raw::c_int;
 use crate::sys::unsupported;
 use crate::sys_common::FromInner;
 use crate::time::Duration;
@@ -115,8 +116,8 @@ impl TcpStream {
     }
 }
 
-impl FromInner<u32> for TcpStream {
-    fn from_inner(fd: u32) -> TcpStream {
+impl FromInner<c_int> for TcpStream {
+    fn from_inner(fd: c_int) -> TcpStream {
         unsafe { TcpStream { fd: WasiFd::from_raw(fd) } }
     }
 }
@@ -181,8 +182,8 @@ impl TcpListener {
     }
 }
 
-impl FromInner<u32> for TcpListener {
-    fn from_inner(fd: u32) -> TcpListener {
+impl FromInner<c_int> for TcpListener {
+    fn from_inner(fd: c_int) -> TcpListener {
         unsafe { TcpListener { fd: WasiFd::from_raw(fd) } }
     }
 }
@@ -331,8 +332,8 @@ impl UdpSocket {
     }
 }
 
-impl FromInner<u32> for UdpSocket {
-    fn from_inner(fd: u32) -> UdpSocket {
+impl FromInner<c_int> for UdpSocket {
+    fn from_inner(fd: c_int) -> UdpSocket {
         unsafe { UdpSocket { fd: WasiFd::from_raw(fd) } }
     }
 }
diff --git a/library/std/src/sys/wasi/stdio.rs b/library/std/src/sys/wasi/stdio.rs
index 209d5b996e5b4..8782f333a1fa4 100644
--- a/library/std/src/sys/wasi/stdio.rs
+++ b/library/std/src/sys/wasi/stdio.rs
@@ -3,6 +3,7 @@
 use super::fd::WasiFd;
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::mem::ManuallyDrop;
+use crate::os::raw;
 
 pub struct Stdin;
 pub struct Stdout;
@@ -14,7 +15,7 @@ impl Stdin {
     }
 
     #[inline]
-    pub fn as_raw_fd(&self) -> u32 {
+    pub fn as_raw_fd(&self) -> raw::c_int {
         0
     }
 }
@@ -40,7 +41,7 @@ impl Stdout {
     }
 
     #[inline]
-    pub fn as_raw_fd(&self) -> u32 {
+    pub fn as_raw_fd(&self) -> raw::c_int {
         1
     }
 }
@@ -69,7 +70,7 @@ impl Stderr {
     }
 
     #[inline]
-    pub fn as_raw_fd(&self) -> u32 {
+    pub fn as_raw_fd(&self) -> raw::c_int {
         2
     }
 }