diff --git a/crates/engine/src/cmd/missing.rs b/crates/engine/src/cmd/missing.rs
index 1bff30d2b..c6c692c35 100644
--- a/crates/engine/src/cmd/missing.rs
+++ b/crates/engine/src/cmd/missing.rs
@@ -197,13 +197,24 @@ impl FindPlan {
     }
 }
 
+/// How Find Missing compares file names: the part after the last `/` or `\`, in lower case. A
+/// library made on Windows keeps Windows paths, whose `\` isn't a separator to `Path` on macOS or
+/// Linux. Files on disk are named by the same rule, so a macOS or Linux file name that holds a
+/// `\` (`a\b.jpg`) still meets its photo, and a `b.jpg` beside it makes that match ambiguous
+/// rather than a guess. With no `a\b.jpg` there, such a photo may be found as `b.jpg`, if the
+/// size on record agrees.
+fn name_key(path: &str) -> String {
+    path.rsplit(['/', '\\']).next().unwrap_or_default().to_lowercase()
+}
+
 /// The file-system half of Find Missing Photos: which `candidates` are gone, and which file in
 /// `folder` (recursively) is each one's. Touches only the disk — never the session — so the app
 /// runs it on a worker thread (walking a big folder on a network share and hashing look-alikes
 /// takes a while) and relinks the result with `library.findMissing {found, missing, ambiguous}`.
 ///
 /// Matching, per photo:
-/// 1. a file with the same name (any letter case), the same size and the same content hash;
+/// 1. a file with the same name ([`name_key`]: any letter case), the same size and the same
+///    content hash;
 /// 2. renamed: a file of the same size with the same content hash (only same-size files are
 ///    read, so this stays cheap);
 /// 3. without a hash to confirm (or the file was edited in place): the one file with the same
@@ -228,8 +239,9 @@ pub fn plan_find_missing(candidates: &[FindCandidate], folder: &str) -> std::res
     let mut by_name: HashMap<String, Vec<String>> = HashMap::new();
     let files: Vec<String> = crate::import::expand(&[folder.to_string()], None).into_iter().filter(|f| !in_use.contains(f.as_str())).collect();
     for f in &files {
-        if let Some(n) = Path::new(f).file_name() {
-            by_name.entry(n.to_string_lossy().to_lowercase()).or_default().push(f.clone());
+        let name = name_key(f);
+        if !name.is_empty() {
+            by_name.entry(name).or_default().push(f.clone());
         }
     }
     let mut by_size: Option<HashMap<u64, Vec<String>>> = None;
@@ -239,7 +251,7 @@ pub fn plan_find_missing(candidates: &[FindCandidate], folder: &str) -> std::res
     let mut used: HashSet<String> = HashSet::new();
     let mut plan = FindPlan::default();
     for c in &lost {
-        let name = Path::new(&c.path).file_name().map(|n| n.to_string_lossy().to_lowercase()).unwrap_or_default();
+        let name = name_key(&c.path);
         let size = c.size;
         let hash = c.hash.as_deref();
         let named: Vec<&String> = by_name
diff --git a/crates/engine/src/tests_import.rs b/crates/engine/src/tests_import.rs
index 191595ebe..a688426ec 100644
--- a/crates/engine/src/tests_import.rs
+++ b/crates/engine/src/tests_import.rs
@@ -263,6 +263,70 @@ fn find_missing_plan_is_rechecked_when_applied() {
     let _ = std::fs::remove_dir_all(&dir);
 }
 
+/// A library made on Windows names its originals with Windows paths; opened on macOS or Linux
+/// they are missing until Find Missing finds them by name, there as everywhere: the name follows
+/// the last `/` or `\`, any letter case, the size checked when one is on record, look-alikes
+/// reported rather than guessed, and undo puts back the path exactly as spelled.
+#[test]
+fn find_missing_finds_the_files_of_a_library_made_on_windows() {
+    use lightcraft_catalog::{Op, Photo, PhotoId, Source};
+    let dir = temp_dir("missing-windows");
+    for (rel, bytes) in [("found/a.jpg", &b"x"[..]), ("found/deep/b.jpg", b"xyz"), ("found/one/twin.jpg", b"x"), ("found/two/twin.jpg", b"x")] {
+        std::fs::create_dir_all(dir.join(rel).parent().unwrap()).unwrap();
+        std::fs::write(dir.join(rel), bytes).unwrap();
+    }
+    let mut s = Session::new();
+    // as a Windows library may list them: no content hash, and a size only for b
+    let mut add = |path: &str, size: u64| {
+        let id = s.catalog.alloc_photo_id();
+        let mut p = Photo::new(id, Source::File { path: path.into() }, "x.jpg", "JPEG", 60, 40, "2026-01-01T10:00:00");
+        p.file_size = size;
+        s.catalog.apply(Op::AddPhoto { photo: Box::new(p) }).unwrap();
+        id
+    };
+    let (a, b, twin) = (add(r"C:\Users\me\Photos\a.jpg", 0), add(r"D:\Shoot\2019\B.JPG", 3), add(r"C:\Users\me\Photos\twin.jpg", 0));
+    let path_of = |s: &Session, id: PhotoId| match &s.catalog.photo(id).unwrap().source {
+        Source::File { path } => path.clone(),
+        _ => String::new(),
+    };
+    let r = s.execute("library.findMissing", &json!({"folder": dir.join("found").to_string_lossy()})).unwrap();
+    assert_eq!(path_of(&s, a), dir.join("found").join("a.jpg").to_string_lossy(), "found by its name: {r}");
+    assert_eq!(path_of(&s, b), dir.join("found").join("deep").join("b.jpg").to_string_lossy(), "found by its name, any case, and size: {r}");
+    assert_eq!(path_of(&s, twin), r"C:\Users\me\Photos\twin.jpg", "two files of its name: not guessed: {r}");
+    assert_eq!(r["ambiguous"][0]["candidates"].as_array().map(Vec::len), Some(2), "both look-alikes reported: {r}");
+    assert_eq!(r["missing"], 1, "{r}");
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert_eq!(
+        (path_of(&s, a), path_of(&s, b)),
+        (r"C:\Users\me\Photos\a.jpg".to_string(), r"D:\Shoot\2019\B.JPG".to_string()),
+        "one undo step puts back the Windows paths as they were spelled"
+    );
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+/// On macOS and Linux `\` may be part of a file name. Find Missing names the files it finds by
+/// the same rule as the missing photos, so `a\b.jpg` isn't relinked to a `b.jpg` beside it
+/// unasked: the two are reported as look-alikes.
+#[cfg(unix)]
+#[test]
+fn find_missing_does_not_take_a_look_alike_for_a_file_name_with_a_backslash() {
+    use lightcraft_catalog::{Op, Photo, Source};
+    let dir = temp_dir("missing-backslash");
+    std::fs::create_dir_all(dir.join("found")).unwrap();
+    for name in [r"a\b.jpg", "b.jpg"] {
+        std::fs::write(dir.join("found").join(name), b"x").unwrap();
+    }
+    let mut s = Session::new();
+    let gone = dir.join("gone").join(r"a\b.jpg").to_string_lossy().to_string();
+    let id = s.catalog.alloc_photo_id();
+    let p = Photo::new(id, Source::File { path: gone.clone() }, "x.jpg", "JPEG", 60, 40, "2026-01-01T10:00:00");
+    s.catalog.apply(Op::AddPhoto { photo: Box::new(p) }).unwrap();
+    let r = s.execute("library.findMissing", &json!({"folder": dir.join("found").to_string_lossy()})).unwrap();
+    assert!(matches!(&s.catalog.photo(id).unwrap().source, Source::File { path } if *path == gone), "not relinked to b.jpg: {r}");
+    assert_eq!(r["ambiguous"][0]["candidates"].as_array().map(Vec::len), Some(2), "both reported: {r}");
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
 #[test]
 fn missing_files_are_found_and_relinked() {
     let dir = std::env::temp_dir().join(format!("lc-missing-{}", std::process::id()));
diff --git a/docs/whats-new.md b/docs/whats-new.md
index dcf203893..41a8c7d14 100644
--- a/docs/whats-new.md
+++ b/docs/whats-new.md
@@ -27,6 +27,14 @@
 - Saving a sidecar keeps another application's properties even when its namespace uses prefixes such as `lc`
   or `xmp`. Those foreign properties no longer become LightCraft settings or ratings when imported.
 
+### Find Missing Photos finds the files of a library made on Windows
+- A library made on Windows records its originals with Windows paths. Opened on macOS or Linux, its photos are
+  missing until relinked, and Find Missing Photos found them only by their content, so it missed every photo it had
+  no fingerprint for (such as photos brought in from a Lightroom catalog) or that had been edited since, even in a
+  folder holding every file under the same name. It now matches them by name as it does any other photo: the name
+  after the last `/` or `\`, in any letter case, checked against the size when the library has one. Several files
+  of that name are still reported rather than guessed, and undo puts back the paths as they were.
+
 ## 2026-10-21
 
 ### Sharper resampling in HDR and panorama merges