diff --git a/src/uu/nl/src/helper.rs b/src/uu/nl/src/helper.rs
index 5841819a406..150de9f8c9e 100644
--- a/src/uu/nl/src/helper.rs
+++ b/src/uu/nl/src/helper.rs
@@ -4,6 +4,8 @@
 // file that was distributed with this source code.
 // spell-checker:ignore (ToDO) conv
 
+use std::ffi::OsString;
+
 use crate::options;
 use uucore::translate;
 
@@ -23,7 +25,7 @@ pub fn parse_options(settings: &mut crate::Settings, opts: &clap::ArgMatches) ->
             delimiter.clone()
         };
     }
-    if let Some(val) = opts.get_one::<String>(options::NUMBER_SEPARATOR) {
+    if let Some(val) = opts.get_one::<OsString>(options::NUMBER_SEPARATOR) {
         settings.number_separator.clone_from(val);
     }
     settings.number_format = opts
diff --git a/src/uu/nl/src/nl.rs b/src/uu/nl/src/nl.rs
index f63be4022d0..15e4629d8dd 100644
--- a/src/uu/nl/src/nl.rs
+++ b/src/uu/nl/src/nl.rs
@@ -34,7 +34,7 @@ pub struct Settings {
     number_format: NumberFormat,
     renumber: bool,
     // The string appended to each line number output.
-    number_separator: String,
+    number_separator: OsString,
 }
 
 impl Default for Settings {
@@ -50,7 +50,7 @@ impl Default for Settings {
             number_width: 6,
             number_format: NumberFormat::Right,
             renumber: true,
-            number_separator: String::from("\t"),
+            number_separator: OsString::from("\t"),
         }
     }
 }
@@ -314,6 +314,7 @@ pub fn uu_app() -> Command {
                 .short('s')
                 .long(options::NUMBER_SEPARATOR)
                 .help(translate!("nl-help-number-separator"))
+                .value_parser(clap::value_parser!(OsString))
                 .value_name("STRING"),
         )
         .arg(
@@ -389,7 +390,7 @@ fn nl<T: Read>(reader: &mut BufReader<T>, stats: &mut Stats, settings: &Settings
                     settings
                         .number_format
                         .format(line_number, settings.number_width),
-                    settings.number_separator,
+                    settings.number_separator.to_string_lossy(),
                 );
                 // update line number for the potential next line
                 match line_number.checked_add(settings.line_increment) {
diff --git a/tests/by-util/test_nl.rs b/tests/by-util/test_nl.rs
index 34a869dbbaa..14b30906dfe 100644
--- a/tests/by-util/test_nl.rs
+++ b/tests/by-util/test_nl.rs
@@ -11,7 +11,7 @@ use uutests::util_name;
 
 #[test]
 #[cfg(target_os = "linux")]
-fn test_nl_non_utf8_paths() {
+fn test_non_utf8_paths() {
     use std::os::unix::ffi::OsStringExt;
     let (at, mut ucmd) = at_and_ucmd!();
 
@@ -209,6 +209,28 @@ fn test_number_separator() {
     }
 }
 
+#[test]
+#[cfg(target_os = "linux")]
+fn test_number_separator_non_utf8() {
+    use std::{
+        ffi::{OsStr, OsString},
+        os::unix::ffi::{OsStrExt, OsStringExt},
+    };
+
+    let separator_bytes = [0xFF, 0xFE];
+    let mut v = b"--number-separator=".to_vec();
+    v.extend_from_slice(&separator_bytes);
+
+    let arg = OsString::from_vec(v);
+    let separator = OsStr::from_bytes(&separator_bytes);
+
+    new_ucmd!()
+        .arg(arg)
+        .pipe_in("test")
+        .succeeds()
+        .stdout_is(format!("     1{}test\n", separator.to_string_lossy()));
+}
+
 #[test]
 fn test_starting_line_number() {
     for arg in ["-v10", "--starting-line-number=10"] {