diff --git a/tests/owned_normalization.rs b/tests/owned_normalization.rs
new file mode 100644
index 0000000..4a88784
--- /dev/null
+++ b/tests/owned_normalization.rs
@@ -0,0 +1,273 @@
+#![cfg(any(target_family = "unix", target_family = "windows"))]
+
+use std::path::{Path, PathBuf};
+
+use sugar_path::SugarPathBuf;
+
+fn assert_owned_normalization(case: &str, input: &str, expected: &str) {
+  let normalized = PathBuf::from(input).into_normalized();
+  assert_eq!(
+    normalized.as_os_str(),
+    Path::new(expected).as_os_str(),
+    "unexpected owned normalization for {case}: {input:?}",
+  );
+
+  let normalized_twice = normalized.clone().into_normalized();
+  assert_eq!(
+    normalized_twice.as_os_str(),
+    normalized.as_os_str(),
+    "owned normalization was not exactly idempotent for {case}: {input:?}",
+  );
+}
+
+#[cfg(target_family = "unix")]
+#[test]
+fn unix_owned_normalization_has_exact_independent_oracles() {
+  let cases = [
+    ("empty", "", "."),
+    ("current directory with redundant separator", ".//", "./"),
+    ("root only", "/", "/"),
+    ("redundant root separators", "////", "/"),
+    ("absolute root clamp", "/a/../../tail/", "/tail/"),
+    ("clean relative", "foo/bar", "foo/bar"),
+    ("clean relative trailing separator", "foo/bar/", "foo/bar/"),
+    ("dirty relative trailing separator", "foo//./bar/../baz//", "foo/baz/"),
+    ("collapse to current directory", "foo/..", "."),
+    ("collapse to current directory with trailing separator", "foo/../", "./"),
+    ("unresolved leading parents", "../../../foo/../bar/", "../../../bar/"),
+    ("backslash is a normal character", r"foo\bar/./baz", r"foo\bar/baz"),
+    ("valid non-ASCII components", "/café/./文件/", "/café/文件/"),
+    (
+      "dirty path beyond the inline component capacity",
+      "a/b/c/d/e/f/g/h/i/../j/",
+      "a/b/c/d/e/f/g/h/j/",
+    ),
+  ];
+
+  for (case, input, expected) in cases {
+    assert_owned_normalization(case, input, expected);
+  }
+}
+
+#[cfg(target_family = "unix")]
+#[test]
+fn non_utf8_unix_owned_normalization_preserves_raw_bytes() {
+  use std::{
+    ffi::OsString,
+    os::unix::ffi::{OsStrExt, OsStringExt},
+  };
+
+  let cases: [(&str, &[u8], &[u8]); 6] = [
+    ("clean relative component", b"dir/invalid-\x80/file", b"dir/invalid-\x80/file"),
+    (
+      "clean absolute component with trailing separator",
+      b"/dir/invalid-\xff/file/",
+      b"/dir/invalid-\xff/file/",
+    ),
+    ("dirty relative component", b"dir/invalid-\x80/./file", b"dir/invalid-\x80/file"),
+    (
+      "unresolved leading parents and trailing separator",
+      b"../../invalid-\xff/./file//",
+      b"../../invalid-\xff/file/",
+    ),
+    ("absolute root clamp", b"/../../invalid-\x80/./file/", b"/invalid-\x80/file/"),
+    ("invalid component removed by a parent", b"dir/invalid-\xff/../", b"dir/"),
+  ];
+
+  for (case, input, expected) in cases {
+    let normalized = PathBuf::from(OsString::from_vec(input.to_vec())).into_normalized();
+    assert_eq!(
+      normalized.as_os_str().as_bytes(),
+      expected,
+      "unexpected owned normalization for {case}",
+    );
+
+    let normalized_twice = normalized.clone().into_normalized();
+    assert_eq!(
+      normalized_twice.as_os_str().as_bytes(),
+      expected,
+      "invalid Unix encoding was not exactly idempotent for {case}",
+    );
+  }
+}
+
+#[cfg(target_family = "windows")]
+#[test]
+fn windows_owned_normalization_has_exact_independent_oracles() {
+  let cases = [
+    ("empty", "", "."),
+    ("current directory with redundant separator", r".\\", r".\"),
+    ("root only", r"\", r"\"),
+    ("root-relative", r"\foo\..\bar\\", r"\bar\"),
+    ("root-relative clamp", r"\..\workspace\pkg\..\dist\", r"\workspace\dist\"),
+    ("clean relative trailing separator", r"foo\bar\", r"foo\bar\"),
+    ("dirty relative trailing separator", r"foo\\.\bar\..\baz\\", r"foo\baz\"),
+    ("unresolved leading parents", r"..\..\pkg\.\src\..\dist\", r"..\..\pkg\dist\"),
+    ("disk prefix only", r"C:", r"C:."),
+    ("disk root", r"c:\", r"c:\"),
+    ("ordinary disk with mixed separators", r"c:/foo//./bar/../", r"c:\foo\"),
+    ("ordinary disk root clamp", r"C:\..\..\foo\", r"C:\foo\"),
+    ("drive-relative", r"C:foo\..\bar\", r"C:bar\"),
+    ("drive-relative unresolved parent", r"c:..\foo\..\bar", r"c:..\bar"),
+    ("drive-relative collapse with trailing separator", r"C:pkg\..\", r"C:.\"),
+    ("ordinary UNC prefix only", r"\\server\share", r"\\server\share\"),
+    (
+      "ordinary UNC root clamp with trailing separator",
+      r"\\server\share\pkg\..\..\file\",
+      r"\\server\share\file\",
+    ),
+    ("verbatim disk prefix only", r"\\?\C:", r"\\?\C:"),
+    ("verbatim disk dirty trailing path", r"\\?\c:\dir\..\file\", r"\\?\c:\file\"),
+    ("verbatim disk rooted collapse", r"\\?\C:\pkg\..", r"\\?\C:\"),
+    ("verbatim disk literal forward slash", r"\\?\C:\foo/", r"\\?\C:\foo/"),
+    ("verbatim disk dirty path with literal forward slash", r"\\?\C:\dir\..\foo/", r"\\?\C:\foo/"),
+    ("verbatim UNC prefix only", r"\\?\UNC\server\share", r"\\?\UNC\server\share"),
+    (
+      "verbatim UNC dirty trailing path",
+      r"\\?\UNC\server\share\dir\..\file\",
+      r"\\?\UNC\server\share\file\",
+    ),
+    (
+      "verbatim UNC literal forward slash",
+      r"\\?\UNC\server\share\pkg\src\..\dist/file",
+      r"\\?\UNC\server\share\pkg\dist/file",
+    ),
+    (
+      "verbatim UNC collapse without trailing separator",
+      r"\\?\UNC\server\share\pkg\..",
+      r"\\?\UNC\server\share",
+    ),
+    (
+      "verbatim UNC collapse with trailing separator",
+      r"\\?\UNC\server\share\pkg\..\",
+      r"\\?\UNC\server\share\",
+    ),
+    ("device namespace prefix only", r"\\.\PIPE", r"\\.\PIPE"),
+    ("device namespace dirty trailing path", r"\\.\PIPE\dir\..\file\", r"\\.\PIPE\file\"),
+    ("device namespace collapse without trailing separator", r"\\.\PIPE\pkg\..", r"\\.\PIPE"),
+    ("device namespace collapse with trailing separator", r"\\.\PIPE\pkg\..\", r"\\.\PIPE\"),
+    ("generic verbatim prefix only", r"\\?\Volume{abc}", r"\\?\Volume{abc}"),
+    (
+      "generic verbatim dirty trailing path",
+      r"\\?\Volume{abc}\dir\..\file\",
+      r"\\?\Volume{abc}\file\",
+    ),
+    (
+      "generic verbatim literal forward slash",
+      r"\\?\Volume{abc}\pkg\src\..\dist/file",
+      r"\\?\Volume{abc}\pkg\dist/file",
+    ),
+    (
+      "generic verbatim collapse without trailing separator",
+      r"\\?\Volume{abc}\pkg\..",
+      r"\\?\Volume{abc}",
+    ),
+    (
+      "generic verbatim collapse with trailing separator",
+      r"\\?\Volume{abc}\pkg\..\",
+      r"\\?\Volume{abc}\",
+    ),
+    ("component must not become a disk prefix", r"dir\..\C:foo", r".\C:foo"),
+    ("prefix-looking component remains normal", r"dir\..\C:", r".\C:"),
+    ("valid non-ASCII components", r"C:\café\.\文件\", r"C:\café\文件\"),
+    (
+      "dirty path beyond the inline component capacity",
+      r"a\b\c\d\e\f\g\h\i\..\j\",
+      r"a\b\c\d\e\f\g\h\j\",
+    ),
+  ];
+
+  for (case, input, expected) in cases {
+    assert_owned_normalization(case, input, expected);
+  }
+}
+
+#[cfg(target_family = "windows")]
+#[test]
+fn non_utf8_windows_owned_normalization_preserves_wide_units() {
+  use std::{
+    ffi::OsString,
+    os::windows::ffi::{OsStrExt, OsStringExt},
+  };
+
+  fn with_invalid_unit(prefix: &str, suffix: &str, invalid: u16) -> Vec<u16> {
+    let mut wide = prefix.encode_utf16().collect::<Vec<_>>();
+    wide.push(invalid);
+    wide.extend(suffix.encode_utf16());
+    wide
+  }
+
+  let cases = [
+    (
+      "clean relative component",
+      with_invalid_unit(r"dir\invalid-", r"\file", 0xd800),
+      with_invalid_unit(r"dir\invalid-", r"\file", 0xd800),
+    ),
+    (
+      "dirty relative component",
+      with_invalid_unit(r"dir\invalid-", r"\.\file", 0xd801),
+      with_invalid_unit(r"dir\invalid-", r"\file", 0xd801),
+    ),
+    (
+      "clean ordinary disk component with trailing separator",
+      with_invalid_unit(r"C:\invalid-", r"\file\", 0xd800),
+      with_invalid_unit(r"C:\invalid-", r"\file\", 0xd800),
+    ),
+    (
+      "unresolved leading parent and trailing separator",
+      with_invalid_unit(r"..\invalid-", r"\.\file\\", 0xd800),
+      with_invalid_unit(r"..\invalid-", r"\file\", 0xd800),
+    ),
+    (
+      "ordinary disk root clamp",
+      with_invalid_unit(r"C:\..\invalid-", r"\.\file\", 0xd801),
+      with_invalid_unit(r"C:\invalid-", r"\file\", 0xd801),
+    ),
+    (
+      "ordinary UNC server identifier",
+      with_invalid_unit(r"\\server-", r"\share\base\.\child\..\file\", 0xd800),
+      with_invalid_unit(r"\\server-", r"\share\base\file\", 0xd800),
+    ),
+    (
+      "ordinary UNC share identifier",
+      with_invalid_unit(r"\\server\share-", r"\base\.\child\..\file\", 0xd801),
+      with_invalid_unit(r"\\server\share-", r"\base\file\", 0xd801),
+    ),
+    (
+      "verbatim UNC server identifier",
+      with_invalid_unit(r"\\?\UNC\server-", r"\share\base\.\child\..\file\", 0xd800),
+      with_invalid_unit(r"\\?\UNC\server-", r"\share\base\file\", 0xd800),
+    ),
+    (
+      "verbatim UNC share identifier",
+      with_invalid_unit(r"\\?\UNC\server\share-", r"\base\.\child\..\file\", 0xd801),
+      with_invalid_unit(r"\\?\UNC\server\share-", r"\base\file\", 0xd801),
+    ),
+    (
+      "device namespace identifier",
+      with_invalid_unit(r"\\.\PIPE-", r"\base\.\child\..\file\", 0xd800),
+      with_invalid_unit(r"\\.\PIPE-", r"\base\file\", 0xd800),
+    ),
+    (
+      "generic verbatim identifier",
+      with_invalid_unit(r"\\?\Volume-", r"\base\.\child\..\file\", 0xd801),
+      with_invalid_unit(r"\\?\Volume-", r"\base\file\", 0xd801),
+    ),
+  ];
+
+  for (case, input, expected) in cases {
+    let normalized = PathBuf::from(OsString::from_wide(&input)).into_normalized();
+    assert_eq!(
+      normalized.as_os_str().encode_wide().collect::<Vec<_>>(),
+      expected,
+      "unexpected owned normalization for {case}",
+    );
+
+    let normalized_twice = normalized.into_normalized();
+    assert_eq!(
+      normalized_twice.as_os_str().encode_wide().collect::<Vec<_>>(),
+      expected,
+      "invalid Windows encoding was not exactly idempotent for {case}",
+    );
+  }
+}