diff --git a/src/uucore/src/lib/features/fs.rs b/src/uucore/src/lib/features/fs.rs
index a15bf0f2b2..99f8a4eb6c 100644
--- a/src/uucore/src/lib/features/fs.rs
+++ b/src/uucore/src/lib/features/fs.rs
@@ -790,23 +790,10 @@ pub fn are_hardlinks_or_one_way_symlink_to_same_file(source: &Path, target: &Pat
 /// * `path` - A reference to the path to be checked.
 #[cfg(any(unix, target_os = "wasi"))]
 pub fn path_ends_with_terminator(path: &Path) -> bool {
-    #[cfg(unix)]
-    use std::os::unix::prelude::OsStrExt;
-    #[cfg(all(target_os = "wasi", target_env = "p1"))]
-    use std::os::wasi::ffi::OsStrExt;
-
-    #[cfg(all(target_os = "wasi", target_env = "p2"))]
-    return path
-        .as_os_str()
+    path.as_os_str()
         .as_encoded_bytes()
         .last()
-        .is_some_and(|&byte| byte == b'/');
-    #[cfg(not(all(target_os = "wasi", target_env = "p2")))]
-    return path
-        .as_os_str()
-        .as_bytes()
-        .last()
-        .is_some_and(|&byte| byte == b'/');
+        .is_some_and(|&byte| byte == b'/')
 }
 
 #[cfg(windows)]
diff --git a/src/uucore/src/lib/lib.rs b/src/uucore/src/lib/lib.rs
index aeacfe01fc..40b2228b5d 100644
--- a/src/uucore/src/lib/lib.rs
+++ b/src/uucore/src/lib/lib.rs
@@ -151,8 +151,6 @@ use std::io::{BufRead, BufReader};
 use std::iter;
 #[cfg(unix)]
 use std::os::unix::ffi::{OsStrExt, OsStringExt};
-#[cfg(all(target_os = "wasi", target_env = "p1"))]
-use std::os::wasi::ffi::{OsStrExt, OsStringExt};
 use std::str;
 use std::str::Utf8Chunk;
 use std::sync::{LazyLock, atomic::Ordering};
@@ -485,15 +483,19 @@ pub fn os_str_as_bytes_lossy(os_string: &OsStr) -> Cow<'_, [u8]> {
 ///
 /// This always succeeds on unix platforms,
 /// and fails on other platforms if the bytes can't be parsed as UTF-8.
-#[cfg_attr(
-    any(unix, all(target_os = "wasi", target_env = "p1")),
-    expect(clippy::unnecessary_wraps)
-)]
+#[cfg_attr(any(unix, target_os = "wasi"), expect(clippy::unnecessary_wraps))]
 pub fn os_str_from_bytes(bytes: &[u8]) -> error::UResult<Cow<'_, OsStr>> {
-    #[cfg(any(unix, all(target_os = "wasi", target_env = "p1")))]
+    #[cfg(unix)]
     return Ok(Cow::Borrowed(OsStr::from_bytes(bytes)));
 
-    #[cfg(not(any(unix, all(target_os = "wasi", target_env = "p1"))))]
+    #[cfg(target_os = "wasi")]
+    return Ok(Cow::Borrowed(
+        // SAFETY: on WASI `OsStr` is a plain byte string with no encoding
+        // invariant, so every byte sequence is a valid `OsStr`.
+        unsafe { OsStr::from_encoded_bytes_unchecked(bytes) },
+    ));
+
+    #[cfg(not(any(unix, target_os = "wasi")))]
     Ok(Cow::Owned(OsString::from(str::from_utf8(bytes).map_err(
         |_| error::UUsageError::new(1, "Unable to transform bytes into OsStr"),
     )?)))
@@ -503,15 +505,17 @@ pub fn os_str_from_bytes(bytes: &[u8]) -> error::UResult<Cow<'_, OsStr>> {
 ///
 /// This always succeeds on unix platforms,
 /// and fails on other platforms if the bytes can't be parsed as UTF-8.
-#[cfg_attr(
-    any(unix, all(target_os = "wasi", target_env = "p1")),
-    expect(clippy::unnecessary_wraps)
-)]
+#[cfg_attr(any(unix, target_os = "wasi"), expect(clippy::unnecessary_wraps))]
 pub fn os_string_from_vec(vec: Vec<u8>) -> error::UResult<OsString> {
-    #[cfg(any(unix, all(target_os = "wasi", target_env = "p1")))]
+    #[cfg(unix)]
     return Ok(OsString::from_vec(vec));
 
-    #[cfg(not(any(unix, all(target_os = "wasi", target_env = "p1"))))]
+    #[cfg(target_os = "wasi")]
+    // SAFETY: on WASI `OsString` is a plain byte string with no encoding
+    // invariant, so every byte sequence is a valid `OsString`.
+    return Ok(unsafe { OsString::from_encoded_bytes_unchecked(vec) });
+
+    #[cfg(not(any(unix, target_os = "wasi")))]
     Ok(OsString::from(String::from_utf8(vec).map_err(|_| {
         error::UUsageError::new(1, "invalid UTF-8 was detected in one or more arguments")
     })?))
@@ -521,14 +525,13 @@ pub fn os_string_from_vec(vec: Vec<u8>) -> error::UResult<OsString> {
 ///
 /// This always succeeds on unix platforms,
 /// and fails on other platforms if the bytes can't be parsed as UTF-8.
-#[cfg_attr(
-    any(unix, all(target_os = "wasi", target_env = "p1")),
-    expect(clippy::unnecessary_wraps)
-)]
+#[cfg_attr(any(unix, target_os = "wasi"), expect(clippy::unnecessary_wraps))]
 pub fn os_string_to_vec(s: OsString) -> error::UResult<Vec<u8>> {
-    #[cfg(any(unix, all(target_os = "wasi", target_env = "p1")))]
+    #[cfg(unix)]
     let v = s.into_vec();
-    #[cfg(not(any(unix, all(target_os = "wasi", target_env = "p1"))))]
+    #[cfg(target_os = "wasi")]
+    let v = s.into_encoded_bytes();
+    #[cfg(not(any(unix, target_os = "wasi")))]
     let v = s
         .into_string()
         .map_err(|_| {
@@ -760,6 +763,35 @@ mod tests {
         test_invalid_utf8_args_ignore(os_str);
     }
 
+    /// On byte-oriented platforms — unix and every WASI environment — the
+    /// `OsString` helpers must round-trip arbitrary bytes, including sequences
+    /// that are not valid UTF-8. This regressed on wasm32-wasip2 and
+    /// wasm32-wasip3, where the conversions fell back to the UTF-8-validating
+    /// path and returned an error instead.
+    #[cfg(any(unix, target_os = "wasi"))]
+    #[test]
+    fn os_string_from_vec_roundtrips_non_utf8() {
+        let source = vec![0x66, 0x6f, 0x80, 0x6f];
+
+        let os_string = os_string_from_vec(source.clone()).unwrap();
+        // The value really does hold bytes that are not valid UTF-8.
+        assert!(os_string.to_str().is_none());
+        assert_eq!(os_string_to_vec(os_string).unwrap(), source);
+    }
+
+    /// Same invariant for the borrowed `OsStr` conversions, which must agree
+    /// with `os_string_from_vec` on what is representable.
+    #[cfg(any(unix, target_os = "wasi"))]
+    #[test]
+    fn os_str_from_bytes_roundtrips_non_utf8() {
+        let source = [0x66, 0x6f, 0x80, 0x6f];
+
+        let os_str = os_str_from_bytes(&source).unwrap();
+        assert!(os_str.to_str().is_none());
+        assert_eq!(os_str_as_bytes(&os_str).unwrap(), &source);
+        assert_eq!(os_str_as_bytes_lossy(&os_str).into_owned(), source);
+    }
+
     #[test]
     fn test_format_usage() {
         assert_eq!(format_usage("expr EXPRESSION"), "expr EXPRESSION");