diff --git a/crates/wasi-c2/cap-std-sync/src/dir.rs b/crates/wasi-c2/cap-std-sync/src/dir.rs
index 42c2b111cc..d4e357e6a7 100644
--- a/crates/wasi-c2/cap-std-sync/src/dir.rs
+++ b/crates/wasi-c2/cap-std-sync/src/dir.rs
@@ -6,7 +6,7 @@ use std::path::{Path, PathBuf};
 use wasi_c2::{
     dir::{ReaddirCursor, ReaddirEntity, WasiDir},
     file::{FdFlags, FileCaps, FileType, Filestat, OFlags, WasiFile},
-    Error,
+    Error, ErrorExt,
 };
 
 pub struct Dir(cap_std::fs::Dir);
@@ -118,7 +118,10 @@ impl WasiDir for Dir {
                 let meta = entry.metadata()?;
                 let inode = meta.ino();
                 let filetype = filetype_from(&meta.file_type());
-                let name = entry.file_name().into_string().map_err(|_| Error::Ilseq)?;
+                let name = entry
+                    .file_name()
+                    .into_string()
+                    .map_err(|_| Error::illegal_byte_sequence().context("filename"))?;
                 let namelen = name.as_bytes().len().try_into()?;
                 Ok((filetype, inode, namelen, name))
             }),
@@ -189,7 +192,7 @@ impl WasiDir for Dir {
         let dest_dir = dest_dir
             .as_any()
             .downcast_ref::<Self>()
-            .ok_or(Error::NotCapable)?;
+            .ok_or(Error::badf().context("failed downcast to cap-std Dir"))?;
         self.0
             .rename(Path::new(src_path), &dest_dir.0, Path::new(dest_path))?;
         Ok(())
@@ -204,7 +207,7 @@ impl WasiDir for Dir {
         let target_dir = target_dir
             .as_any()
             .downcast_ref::<Self>()
-            .ok_or(Error::NotCapable)?;
+            .ok_or(Error::badf().context("failed downcast to cap-std Dir"))?;
         let src_path = Path::new(src_path);
         let target_path = Path::new(target_path);
         self.0.hard_link(src_path, &target_dir.0, target_path)?;
diff --git a/crates/wasi-c2/cap-std-sync/src/file.rs b/crates/wasi-c2/cap-std-sync/src/file.rs
index 00a43dd3eb..0089af7779 100644
--- a/crates/wasi-c2/cap-std-sync/src/file.rs
+++ b/crates/wasi-c2/cap-std-sync/src/file.rs
@@ -77,26 +77,26 @@ impl WasiFile for File {
     }
     fn read_vectored(&self, bufs: &mut [io::IoSliceMut]) -> Result<u64, Error> {
         let n = self.0.read_vectored(bufs)?;
-        Ok(n.try_into().map_err(|_| Error::Overflow)?)
+        Ok(n.try_into()?)
     }
     fn read_vectored_at(&self, bufs: &mut [io::IoSliceMut], offset: u64) -> Result<u64, Error> {
         let n = self.0.read_vectored_at(bufs, offset)?;
-        Ok(n.try_into().map_err(|_| Error::Overflow)?)
+        Ok(n.try_into()?)
     }
     fn write_vectored(&self, bufs: &[io::IoSlice]) -> Result<u64, Error> {
         let n = self.0.write_vectored(bufs)?;
-        Ok(n.try_into().map_err(|_| Error::Overflow)?)
+        Ok(n.try_into()?)
     }
     fn write_vectored_at(&self, bufs: &[io::IoSlice], offset: u64) -> Result<u64, Error> {
         let n = self.0.write_vectored_at(bufs, offset)?;
-        Ok(n.try_into().map_err(|_| Error::Overflow)?)
+        Ok(n.try_into()?)
     }
     fn seek(&self, pos: std::io::SeekFrom) -> Result<u64, Error> {
         Ok(self.0.seek(pos)?)
     }
     fn peek(&self, buf: &mut [u8]) -> Result<u64, Error> {
         let n = self.0.peek(buf)?;
-        Ok(n.try_into().map_err(|_| Error::Overflow)?)
+        Ok(n.try_into()?)
     }
     fn num_ready_bytes(&self) -> Result<u64, Error> {
         Ok(self.0.num_ready_bytes()?)
diff --git a/crates/wasi-c2/cap-std-sync/src/sched/unix.rs b/crates/wasi-c2/cap-std-sync/src/sched/unix.rs
index 20c4c61ce7..24ce8b251f 100644
--- a/crates/wasi-c2/cap-std-sync/src/sched/unix.rs
+++ b/crates/wasi-c2/cap-std-sync/src/sched/unix.rs
@@ -8,7 +8,7 @@ use wasi_c2::{
         subscription::{RwEventFlags, Subscription},
         Poll, WasiSched,
     },
-    Error,
+    Error, ErrorExt,
 };
 
 use poll::{PollFd, PollFlags};
@@ -25,12 +25,16 @@ impl WasiSched for SyncSched {
         for s in poll.rw_subscriptions() {
             match s {
                 Subscription::Read(f) => {
-                    let raw_fd = wasi_file_raw_fd(f.file.deref()).ok_or(Error::Inval)?;
+                    let raw_fd = wasi_file_raw_fd(f.file.deref()).ok_or(
+                        Error::invalid_argument().context("read subscription fd downcast failed"),
+                    )?;
                     pollfds.push(unsafe { PollFd::new(raw_fd, PollFlags::POLLIN) });
                 }
 
                 Subscription::Write(f) => {
-                    let raw_fd = wasi_file_raw_fd(f.file.deref()).ok_or(Error::Inval)?;
+                    let raw_fd = wasi_file_raw_fd(f.file.deref()).ok_or(
+                        Error::invalid_argument().context("write subscription fd downcast failed"),
+                    )?;
                     pollfds.push(unsafe { PollFd::new(raw_fd, PollFlags::POLLOUT) });
                 }
                 Subscription::MonotonicClock { .. } => unreachable!(),
@@ -45,7 +49,7 @@ impl WasiSched for SyncSched {
                     .unwrap_or(Duration::from_secs(0));
                 (duration.as_millis() + 1) // XXX try always rounding up?
                     .try_into()
-                    .map_err(|_| Error::Overflow)?
+                    .map_err(|_| Error::overflow().context("poll timeout"))?
             } else {
                 libc::c_int::max_value()
             };
@@ -78,9 +82,9 @@ impl WasiSched for SyncSched {
                         _ => unreachable!(),
                     };
                     if revents.contains(PollFlags::POLLNVAL) {
-                        rwsub.error(Error::Badf);
+                        rwsub.error(Error::badf());
                     } else if revents.contains(PollFlags::POLLERR) {
-                        rwsub.error(Error::Io);
+                        rwsub.error(Error::io());
                     } else if revents.contains(PollFlags::POLLHUP) {
                         rwsub.complete(nbytes, RwEventFlags::HANGUP);
                     } else {
diff --git a/crates/wasi-c2/cap-std-sync/src/stdio.rs b/crates/wasi-c2/cap-std-sync/src/stdio.rs
index 13026e5b70..935f37a4da 100644
--- a/crates/wasi-c2/cap-std-sync/src/stdio.rs
+++ b/crates/wasi-c2/cap-std-sync/src/stdio.rs
@@ -13,7 +13,7 @@ use std::os::windows::io::{AsRawHandle, RawHandle};
 use unsafe_io::AsUnsafeFile;
 use wasi_c2::{
     file::{FdFlags, FileType, Filestat, WasiFile},
-    Error,
+    Error, ErrorExt,
 };
 
 pub struct Stdin(std::io::Stdin);
@@ -40,7 +40,7 @@ impl WasiFile for Stdin {
         Ok(FdFlags::empty())
     }
     unsafe fn reopen_with_fdflags(&self, _fdflags: FdFlags) -> Result<Box<dyn WasiFile>, Error> {
-        Err(Error::Badf)
+        Err(Error::badf())
     }
     fn get_filestat(&self) -> Result<Filestat, Error> {
         let meta = self.0.as_file_view().metadata()?;
@@ -56,32 +56,32 @@ impl WasiFile for Stdin {
         })
     }
     fn set_filestat_size(&self, _size: u64) -> Result<(), Error> {
-        Err(Error::Badf)
+        Err(Error::badf())
     }
     fn advise(&self, _offset: u64, _len: u64, _advice: Advice) -> Result<(), Error> {
-        Err(Error::Badf)
+        Err(Error::badf())
     }
     fn allocate(&self, _offset: u64, _len: u64) -> Result<(), Error> {
-        Err(Error::Badf)
+        Err(Error::badf())
     }
     fn read_vectored(&self, bufs: &mut [io::IoSliceMut]) -> Result<u64, Error> {
         let n = self.0.as_file_view().read_vectored(bufs)?;
-        Ok(n.try_into().map_err(|_| Error::Overflow)?)
+        Ok(n.try_into().map_err(|_| Error::range())?)
     }
     fn read_vectored_at(&self, _bufs: &mut [io::IoSliceMut], _offset: u64) -> Result<u64, Error> {
-        Err(Error::Spipe)
+        Err(Error::seek_pipe())
     }
     fn write_vectored(&self, _bufs: &[io::IoSlice]) -> Result<u64, Error> {
-        Err(Error::Badf)
+        Err(Error::badf())
     }
     fn write_vectored_at(&self, _bufs: &[io::IoSlice], _offset: u64) -> Result<u64, Error> {
-        Err(Error::Badf)
+        Err(Error::badf())
     }
     fn seek(&self, _pos: std::io::SeekFrom) -> Result<u64, Error> {
-        Err(Error::Spipe)
+        Err(Error::seek_pipe())
     }
     fn peek(&self, _buf: &mut [u8]) -> Result<u64, Error> {
-        Err(Error::Spipe)
+        Err(Error::seek_pipe())
     }
     fn set_times(
         &self,
@@ -132,7 +132,7 @@ macro_rules! wasi_file_write_impl {
                 &self,
                 _fdflags: FdFlags,
             ) -> Result<Box<dyn WasiFile>, Error> {
-                Err(Error::Badf)
+                Err(Error::badf())
             }
             fn get_filestat(&self) -> Result<Filestat, Error> {
                 let meta = self.0.as_file_view().metadata()?;
@@ -148,36 +148,36 @@ macro_rules! wasi_file_write_impl {
                 })
             }
             fn set_filestat_size(&self, _size: u64) -> Result<(), Error> {
-                Err(Error::Badf)
+                Err(Error::badf())
             }
             fn advise(&self, _offset: u64, _len: u64, _advice: Advice) -> Result<(), Error> {
-                Err(Error::Badf)
+                Err(Error::badf())
             }
             fn allocate(&self, _offset: u64, _len: u64) -> Result<(), Error> {
-                Err(Error::Badf)
+                Err(Error::badf())
             }
             fn read_vectored(&self, _bufs: &mut [io::IoSliceMut]) -> Result<u64, Error> {
-                Err(Error::Badf)
+                Err(Error::badf())
             }
             fn read_vectored_at(
                 &self,
                 _bufs: &mut [io::IoSliceMut],
                 _offset: u64,
             ) -> Result<u64, Error> {
-                Err(Error::Badf)
+                Err(Error::badf())
             }
             fn write_vectored(&self, bufs: &[io::IoSlice]) -> Result<u64, Error> {
                 let n = self.0.as_file_view().write_vectored(bufs)?;
-                Ok(n.try_into().map_err(|_| Error::Overflow)?)
+                Ok(n.try_into().map_err(|c| Error::range().context(c))?)
             }
             fn write_vectored_at(&self, _bufs: &[io::IoSlice], _offset: u64) -> Result<u64, Error> {
-                Err(Error::Spipe)
+                Err(Error::seek_pipe())
             }
             fn seek(&self, _pos: std::io::SeekFrom) -> Result<u64, Error> {
-                Err(Error::Spipe)
+                Err(Error::seek_pipe())
             }
             fn peek(&self, _buf: &mut [u8]) -> Result<u64, Error> {
-                Err(Error::Badf)
+                Err(Error::badf())
             }
             fn set_times(
                 &self,
diff --git a/crates/wasi-c2/src/error.rs b/crates/wasi-c2/src/error.rs
index 9ff237ce6c..44bcab1795 100644
--- a/crates/wasi-c2/src/error.rs
+++ b/crates/wasi-c2/src/error.rs
@@ -21,6 +21,9 @@ pub enum ErrorKind {
     /// Errno::Inval: Invalid argument
     #[error("Inval: Invalid argument")]
     Inval,
+    /// Errno::Io: I/O error
+    #[error("Io: I/O error")]
+    Io,
     /// Errno::Nametoolong: Filename too long
     #[error("Nametoolong: Filename too long")]
     Nametoolong,
@@ -50,6 +53,7 @@ pub trait ErrorExt {
     fn exist() -> Self;
     fn illegal_byte_sequence() -> Self;
     fn invalid_argument() -> Self;
+    fn io() -> Self;
     fn name_too_long() -> Self;
     fn not_dir() -> Self;
     fn not_supported() -> Self;
@@ -75,6 +79,9 @@ impl ErrorExt for Error {
     fn invalid_argument() -> Self {
         ErrorKind::Inval.into()
     }
+    fn io() -> Self {
+        ErrorKind::Io.into()
+    }
     fn name_too_long() -> Self {
         ErrorKind::Nametoolong.into()
     }
diff --git a/crates/wasi-c2/src/snapshots/preview_1.rs b/crates/wasi-c2/src/snapshots/preview_1.rs
index 73f539de9a..ac698ff3b4 100644
--- a/crates/wasi-c2/src/snapshots/preview_1.rs
+++ b/crates/wasi-c2/src/snapshots/preview_1.rs
@@ -79,6 +79,7 @@ impl From<ErrorKind> for types::Errno {
             ErrorKind::Exist => Errno::Exist,
             ErrorKind::Ilseq => Errno::Ilseq,
             ErrorKind::Inval => Errno::Inval,
+            ErrorKind::Io => Errno::Io,
             ErrorKind::Nametoolong => Errno::Nametoolong,
             ErrorKind::Notdir => Errno::Notdir,
             ErrorKind::Notsup => Errno::Notsup,
@@ -141,9 +142,15 @@ impl TryFrom<std::io::Error> for types::Errno {
                 libc::EOVERFLOW => Ok(types::Errno::Overflow),
                 libc::EILSEQ => Ok(types::Errno::Ilseq),
                 libc::ENOTSUP => Ok(types::Errno::Notsup),
-                _ => Err(anyhow!(err).context("Unknown raw OS error")),
+                code => Err(anyhow!(err).context(format!("Unknown raw OS error: {}", code))),
+            },
+            None => match err.kind() {
+                std::io::ErrorKind::NotFound => Ok(types::Errno::Noent),
+                std::io::ErrorKind::PermissionDenied => Ok(types::Errno::Perm),
+                std::io::ErrorKind::AlreadyExists => Ok(types::Errno::Exist),
+                std::io::ErrorKind::InvalidInput => Ok(types::Errno::Ilseq),
+                k => Err(anyhow!(err).context(format!("No raw OS error. Unhandled kind: {:?}", k))),
             },
-            None => Err(anyhow!(err).context("No raw OS error")),
         }
     }
 }