diff --git a/src/uu/nl/src/helper.rs b/src/uu/nl/src/helper.rs
index 44f5fa750..6bbec85f4 100644
--- a/src/uu/nl/src/helper.rs
+++ b/src/uu/nl/src/helper.rs
@@ -16,11 +16,13 @@ pub fn parse_options(settings: &mut crate::Settings, opts: &clap::ArgMatches) ->
     // This vector holds error messages encountered.
     let mut errs: Vec<String> = vec![];
     settings.renumber = opts.get_flag(options::NO_RENUMBER);
-    if let Some(delimiter) = opts.get_one::<String>(options::SECTION_DELIMITER) {
-        // check whether the delimiter is a single ASCII char (1 byte)
-        // because GNU nl doesn't add a ':' to single non-ASCII chars
+    if let Some(delimiter) = opts.get_one::<OsString>(options::SECTION_DELIMITER) {
+        // GNU nl determines whether a delimiter is a "single character" based on byte length, not
+        // character length. A "single character" implies the second character is a ':'.
         settings.section_delimiter = if delimiter.len() == 1 {
-            format!("{delimiter}:")
+            let mut delimiter = delimiter.clone();
+            delimiter.push(":");
+            delimiter
         } else {
             delimiter.clone()
         };
diff --git a/src/uu/nl/src/nl.rs b/src/uu/nl/src/nl.rs
index 56a390d9c..261d7897f 100644
--- a/src/uu/nl/src/nl.rs
+++ b/src/uu/nl/src/nl.rs
@@ -4,7 +4,7 @@
 // file that was distributed with this source code.
 
 use clap::{Arg, ArgAction, Command};
-use std::ffi::OsString;
+use std::ffi::{OsStr, OsString};
 use std::fs::File;
 use std::io::{BufRead, BufReader, Read, stdin};
 use std::path::Path;
@@ -20,7 +20,7 @@ pub struct Settings {
     body_numbering: NumberingStyle,
     footer_numbering: NumberingStyle,
     // The variable corresponding to -d
-    section_delimiter: String,
+    section_delimiter: OsString,
     // The variables corresponding to the options -v, -i, -l, -w.
     starting_line_number: i64,
     line_increment: i64,
@@ -40,7 +40,7 @@ impl Default for Settings {
             header_numbering: NumberingStyle::None,
             body_numbering: NumberingStyle::NonEmpty,
             footer_numbering: NumberingStyle::None,
-            section_delimiter: String::from("\\:"),
+            section_delimiter: OsString::from("\\:"),
             starting_line_number: 1,
             line_increment: 1,
             join_blank_lines: 1,
@@ -140,8 +140,8 @@ enum SectionDelimiter {
 impl SectionDelimiter {
     /// A valid section delimiter contains the pattern one to three times,
     /// and nothing else.
-    fn parse(bytes: &[u8], pattern: &str) -> Option<Self> {
-        let pattern = pattern.as_bytes();
+    fn parse(bytes: &[u8], pattern: &OsStr) -> Option<Self> {
+        let pattern = pattern.as_encoded_bytes();
 
         if bytes.is_empty() || pattern.is_empty() || bytes.len() % pattern.len() != 0 {
             return None;
@@ -270,6 +270,7 @@ pub fn uu_app() -> Command {
                 .short('d')
                 .long(options::SECTION_DELIMITER)
                 .help(translate!("nl-help-section-delimiter"))
+                .value_parser(clap::value_parser!(OsString))
                 .value_name("CC"),
         )
         .arg(
diff --git a/tests/by-util/test_nl.rs b/tests/by-util/test_nl.rs
index 03e98cbcd..953d7bcb3 100644
--- a/tests/by-util/test_nl.rs
+++ b/tests/by-util/test_nl.rs
@@ -627,7 +627,50 @@ fn test_section_delimiter() {
 }
 
 #[test]
-fn test_one_char_section_delimiter_expansion() {
+#[cfg(target_os = "linux")]
+fn test_section_delimiter_non_utf8() {
+    use std::{ffi::OsString, os::unix::ffi::OsStringExt};
+
+    fn create_arg(prefix: &[u8]) -> OsString {
+        let section_delimiter = [0xFF, 0xFE];
+        let mut v = prefix.to_vec();
+        v.extend_from_slice(&section_delimiter);
+        OsString::from_vec(v)
+    }
+
+    let short = create_arg(b"-d");
+    let long = create_arg(b"--section-delimiter=");
+
+    for arg in [short, long] {
+        let header_section: Vec<u8> =
+            vec![b'a', b'\n', 0xFF, 0xFE, 0xFF, 0xFE, 0xFF, 0xFE, b'\n', b'b'];
+
+        new_ucmd!()
+            .arg(&arg)
+            .pipe_in(header_section)
+            .succeeds()
+            .stdout_is("     1\ta\n\n       b\n");
+
+        let body_section: Vec<u8> = vec![b'a', b'\n', 0xFF, 0xFE, 0xFF, 0xFE, b'\n', b'b'];
+
+        new_ucmd!()
+            .arg(&arg)
+            .pipe_in(body_section)
+            .succeeds()
+            .stdout_is("     1\ta\n\n     1\tb\n");
+
+        let footer_section: Vec<u8> = vec![b'a', b'\n', 0xFF, 0xFE, b'\n', b'b'];
+
+        new_ucmd!()
+            .arg(&arg)
+            .pipe_in(footer_section)
+            .succeeds()
+            .stdout_is("     1\ta\n\n       b\n");
+    }
+}
+
+#[test]
+fn test_one_char_section_delimiter() {
     for arg in ["-da", "--section-delimiter=a"] {
         new_ucmd!()
             .arg(arg)
@@ -649,6 +692,48 @@ fn test_one_char_section_delimiter_expansion() {
     }
 }
 
+#[test]
+#[cfg(target_os = "linux")]
+fn test_one_byte_section_delimiter() {
+    use std::{ffi::OsString, os::unix::ffi::OsStringExt};
+
+    fn create_arg(prefix: &[u8]) -> OsString {
+        let mut v = prefix.to_vec();
+        v.push(0xFF);
+        OsString::from_vec(v)
+    }
+
+    let short = create_arg(b"-d");
+    let long = create_arg(b"--section-delimiter=");
+
+    for arg in [short, long] {
+        let header_section: Vec<u8> =
+            vec![b'a', b'\n', 0xFF, b':', 0xFF, b':', 0xFF, b':', b'\n', b'b'];
+
+        new_ucmd!()
+            .arg(&arg)
+            .pipe_in(header_section)
+            .succeeds()
+            .stdout_is("     1\ta\n\n       b\n");
+
+        let body_section: Vec<u8> = vec![b'a', b'\n', 0xFF, b':', 0xFF, b':', b'\n', b'b'];
+
+        new_ucmd!()
+            .arg(&arg)
+            .pipe_in(body_section)
+            .succeeds()
+            .stdout_is("     1\ta\n\n     1\tb\n");
+
+        let footer_section: Vec<u8> = vec![b'a', b'\n', 0xFF, b':', b'\n', b'b'];
+
+        new_ucmd!()
+            .arg(&arg)
+            .pipe_in(footer_section)
+            .succeeds()
+            .stdout_is("     1\ta\n\n       b\n");
+    }
+}
+
 #[test]
 fn test_non_ascii_one_char_section_delimiter() {
     for arg in ["-dä", "--section-delimiter=ä"] {