diff --git a/src/hostcalls/fs.rs b/src/hostcalls/fs.rs
index 1ad510b3ff..b75617b183 100644
--- a/src/hostcalls/fs.rs
+++ b/src/hostcalls/fs.rs
@@ -7,7 +7,7 @@ use crate::sys::{errno_from_host, host_impl, hostcalls_impl};
 use crate::{host, wasm32};
 use log::trace;
 use std::convert::identity;
-use std::io::{self, Read, Write};
+use std::io::{self, Read, Seek, SeekFrom, Write};
 
 use wasi_common_cbindgen::wasi_common_cbindgen;
 
@@ -299,7 +299,7 @@ pub fn fd_seek(
     } else {
         host::__WASI_RIGHT_FD_SEEK | host::__WASI_RIGHT_FD_TELL
     };
-    let fd = match wasi_ctx
+    let mut fd = match wasi_ctx
         .get_fd_entry(fd, rights, 0)
         .and_then(|fe| fe.fd_object.descriptor.as_file())
     {
@@ -307,8 +307,17 @@ pub fn fd_seek(
         Err(e) => return return_enc_errno(e),
     };
 
-    let host_newoffset = match hostcalls_impl::fd_seek(fd, offset, whence) {
-        Ok(host_newoffset) => host_newoffset,
+    let pos = match whence {
+        host::__WASI_WHENCE_CUR => SeekFrom::Current(offset),
+        host::__WASI_WHENCE_END => SeekFrom::End(offset),
+        host::__WASI_WHENCE_SET => SeekFrom::Start(offset as u64),
+        _ => return return_enc_errno(host::__WASI_EINVAL),
+    };
+    let host_newoffset = match fd
+        .seek(pos)
+        .map_err(|err| err.raw_os_error().map_or(host::__WASI_EIO, errno_from_host))
+    {
+        Ok(offset) => offset,
         Err(e) => return return_enc_errno(e),
     };
 
diff --git a/src/sys/unix/hostcalls_impl/fs.rs b/src/sys/unix/hostcalls_impl/fs.rs
index 4265173373..9d3d9bc253 100644
--- a/src/sys/unix/hostcalls_impl/fs.rs
+++ b/src/sys/unix/hostcalls_impl/fs.rs
@@ -27,25 +27,6 @@ pub(crate) fn fd_pwrite(file: &File, buf: &[u8], offset: host::__wasi_filesize_t
         .map_err(|e| e.raw_os_error().map_or(host::__WASI_EIO, errno_from_host))
 }
 
-pub(crate) fn fd_seek(
-    file: &File,
-    offset: host::__wasi_filedelta_t,
-    whence: host::__wasi_whence_t,
-) -> Result<u64> {
-    use nix::unistd::{lseek, Whence};
-    let nwhence = match whence {
-        host::__WASI_WHENCE_CUR => Whence::SeekCur,
-        host::__WASI_WHENCE_END => Whence::SeekEnd,
-        host::__WASI_WHENCE_SET => Whence::SeekSet,
-        _ => return Err(host::__WASI_EINVAL),
-    };
-
-    match lseek(file.as_raw_fd(), offset, nwhence) {
-        Ok(offset) => Ok(offset as u64),
-        Err(e) => Err(host_impl::errno_from_nix(e.as_errno().unwrap())),
-    }
-}
-
 pub(crate) fn fd_tell(file: &File) -> Result<u64> {
     use nix::unistd::{lseek, Whence};
     match lseek(file.as_raw_fd(), 0, Whence::SeekCur) {
diff --git a/src/sys/windows/hostcalls_impl/fs.rs b/src/sys/windows/hostcalls_impl/fs.rs
index 7a7d882f88..b696694ce0 100644
--- a/src/sys/windows/hostcalls_impl/fs.rs
+++ b/src/sys/windows/hostcalls_impl/fs.rs
@@ -46,14 +46,6 @@ pub(crate) fn fd_pwrite(file: &File, buf: &[u8], offset: host::__wasi_filesize_t
         .map_err(|err| err.raw_os_error().map_or(host::__WASI_EIO, errno_from_host))
 }
 
-pub(crate) fn fd_seek(
-    file: &File,
-    offset: host::__wasi_filedelta_t,
-    whence: host::__wasi_whence_t,
-) -> Result<u64> {
-    unimplemented!("fd_seek")
-}
-
 pub(crate) fn fd_tell(file: &File) -> Result<u64> {
     unimplemented!("fd_tell")
 }