diff --git a/src/context_diff.rs b/src/context_diff.rs
index 334a661..f0f2710 100644
--- a/src/context_diff.rs
+++ b/src/context_diff.rs
@@ -8,7 +8,9 @@ use std::io::Write;
 
 use crate::params::Params;
 use crate::utils::do_write_line;
-use crate::utils::{get_modification_time, is_posix_locale, FunctionLineFinder, TimestampStyle};
+use crate::utils::{
+    get_modification_time, is_posix_locale, write_file_header, FunctionLineFinder, TimestampStyle,
+};
 
 #[derive(Debug, PartialEq)]
 pub enum DiffLine {
@@ -323,14 +325,9 @@ pub fn diff(expected: &[u8], actual: &[u8], params: &Params) -> Vec<u8> {
     };
     let from_modified_time = get_modification_time(&params.from.to_string_lossy(), style);
     let to_modified_time = get_modification_time(&params.to.to_string_lossy(), style);
-    let mut output = format!(
-        "*** {0}\t{1}\n--- {2}\t{3}\n",
-        params.from.to_string_lossy(),
-        from_modified_time,
-        params.to.to_string_lossy(),
-        to_modified_time
-    )
-    .into_bytes();
+    let mut output = Vec::new();
+    write_file_header(&mut output, "***", &params.from, &from_modified_time);
+    write_file_header(&mut output, "---", &params.to, &to_modified_time);
     let diff_results = make_diff(expected, actual, params.context_count, params.brief);
     if diff_results.is_empty() {
         return Vec::new();
diff --git a/src/dir_diff.rs b/src/dir_diff.rs
index d389bf4..a7a8505 100644
--- a/src/dir_diff.rs
+++ b/src/dir_diff.rs
@@ -14,7 +14,7 @@ use std::path::{Path, PathBuf};
 
 use crate::diff::{compare_files, Outcome};
 use crate::params::{MissingFile, Params};
-use crate::utils::report_failure_to_read_input_file;
+use crate::utils::{quote_file_name, quote_shell_argument, report_failure_to_read_input_file};
 
 /// Compares the directories `params.from` and `params.to`. `option_args` are
 /// the command line options, repeated in the header printed before the
@@ -177,14 +177,13 @@ impl DirectoryWalker<'_> {
             ..self.params.clone()
         };
         let mut header = b"diff".to_vec();
-        for arg in self
-            .option_args
-            .iter()
-            .map(OsString::as_os_str)
-            .chain([from, to])
-        {
+        for arg in self.option_args {
             header.push(b' ');
-            header.extend_from_slice(arg.as_encoded_bytes());
+            header.extend_from_slice(&quote_shell_argument(arg.as_encoded_bytes()));
+        }
+        for path in [from, to] {
+            header.push(b' ');
+            header.extend_from_slice(&quote_file_name(path.as_encoded_bytes()));
         }
         header.push(b'\n');
         compare_files(&params, Some(&header))
diff --git a/src/unified_diff.rs b/src/unified_diff.rs
index 094b4e1..e30da1d 100644
--- a/src/unified_diff.rs
+++ b/src/unified_diff.rs
@@ -8,7 +8,7 @@ use std::io::Write;
 
 use crate::params::Params;
 use crate::utils::do_write_line;
-use crate::utils::{get_modification_time, FunctionLineFinder, TimestampStyle};
+use crate::utils::{get_modification_time, write_file_header, FunctionLineFinder, TimestampStyle};
 
 #[derive(Debug, PartialEq)]
 pub enum DiffLine {
@@ -245,14 +245,9 @@ pub fn diff(expected: &[u8], actual: &[u8], params: &Params) -> Vec<u8> {
     let from_modified_time =
         get_modification_time(&params.from.to_string_lossy(), TimestampStyle::Iso);
     let to_modified_time = get_modification_time(&params.to.to_string_lossy(), TimestampStyle::Iso);
-    let mut output = format!(
-        "--- {0}\t{1}\n+++ {2}\t{3}\n",
-        params.from.to_string_lossy(),
-        from_modified_time,
-        params.to.to_string_lossy(),
-        to_modified_time
-    )
-    .into_bytes();
+    let mut output = Vec::new();
+    write_file_header(&mut output, "---", &params.from, &from_modified_time);
+    write_file_header(&mut output, "+++", &params.to, &to_modified_time);
     let diff_results = make_diff(expected, actual, params.context_count, params.brief);
     if diff_results.is_empty() {
         return Vec::new();
diff --git a/src/utils.rs b/src/utils.rs
index 8e35bc9..0265109 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -5,7 +5,11 @@
 
 use crate::bre::Bre;
 use regex::Regex;
-use std::{ffi::OsString, io::Write};
+use std::{
+    borrow::Cow,
+    ffi::{OsStr, OsString},
+    io::Write,
+};
 use unicode_width::UnicodeWidthStr;
 
 /// Replace tabs by spaces in the input line.
@@ -53,6 +57,96 @@ pub fn do_write_line(
     }
 }
 
+/// Quotes a file name for the headers of the diff output: a name containing
+/// spaces, double quotes, backslashes, control characters or non-ASCII bytes
+/// is written between double quotes with C-style escapes, other names are
+/// written as is. On Windows, backslashes separate path components and are
+/// left alone.
+#[must_use]
+pub fn quote_file_name(name: &[u8]) -> Cow<'_, [u8]> {
+    const SPECIAL_BACKSLASH: bool = cfg!(not(windows));
+    let needs_quotes = |byte: u8| {
+        byte <= b' ' || byte == b'"' || (byte == b'\\' && SPECIAL_BACKSLASH) || byte >= 0x80
+    };
+    if !name.iter().copied().any(needs_quotes) {
+        return Cow::Borrowed(name);
+    }
+    let mut quoted = Vec::with_capacity(name.len() + 8);
+    quoted.push(b'"');
+    for &byte in name {
+        let escape = match byte {
+            b'"' => b'"',
+            b'\\' if SPECIAL_BACKSLASH => b'\\',
+            0x07 => b'a',
+            0x08 => b'b',
+            b'\t' => b't',
+            b'\n' => b'n',
+            0x0b => b'v',
+            0x0c => b'f',
+            b'\r' => b'r',
+            b' ' => {
+                quoted.push(b' ');
+                continue;
+            }
+            byte if needs_quotes(byte) => {
+                quoted.extend_from_slice(format!("\\{byte:03o}").as_bytes());
+                continue;
+            }
+            byte => {
+                quoted.push(byte);
+                continue;
+            }
+        };
+        quoted.extend_from_slice(&[b'\\', escape]);
+    }
+    quoted.push(b'"');
+    Cow::Owned(quoted)
+}
+
+/// Appends a file header line of the context or unified formats, such as
+/// `--- name\ttimestamp`, to `output`.
+pub fn write_file_header(output: &mut Vec<u8>, marker: &str, name: &OsStr, timestamp: &str) {
+    output.extend_from_slice(marker.as_bytes());
+    output.push(b' ');
+    output.extend_from_slice(&quote_file_name(name.as_encoded_bytes()));
+    output.push(b'\t');
+    output.extend_from_slice(timestamp.as_bytes());
+    output.push(b'\n');
+}
+
+/// Quotes a command line argument the way a shell would need it, for the
+/// headers that repeat the options of a directory comparison.
+#[must_use]
+pub fn quote_shell_argument(arg: &[u8]) -> Cow<'_, [u8]> {
+    const SPECIAL: &[u8] = b"^*?!=()|&;<>`\\'\"$[";
+    let is_special = |byte: &u8| *byte <= b' ' || *byte == 0x7f || SPECIAL.contains(byte);
+    let special_start = matches!(arg.first(), Some(b'~' | b'#'));
+    if !special_start && !arg.iter().any(is_special) && !arg.is_empty() {
+        return Cow::Borrowed(arg);
+    }
+    let mut quoted = Vec::with_capacity(arg.len() + 2);
+    let only_single_quotes = arg
+        .iter()
+        .filter(|byte| is_special(byte))
+        .all(|&byte| byte == b'\'');
+    if arg.contains(&b'\'') && only_single_quotes {
+        quoted.push(b'"');
+        quoted.extend_from_slice(arg);
+        quoted.push(b'"');
+    } else {
+        quoted.push(b'\'');
+        for &byte in arg {
+            if byte == b'\'' {
+                quoted.extend_from_slice(b"'\\''");
+            } else {
+                quoted.push(byte);
+            }
+        }
+        quoted.push(b'\'');
+    }
+    Cow::Owned(quoted)
+}
+
 /// Finds the lines shown after hunk headers by `-F` and `-p`: the nearest
 /// line of the old file preceding a hunk that matches one of the patterns.
 pub struct FunctionLineFinder<'a> {
@@ -309,6 +403,54 @@ mod tests {
         }
     }
 
+    mod quoting {
+        use super::*;
+        use pretty_assertions::assert_eq;
+
+        fn quoted_name(name: &[u8]) -> String {
+            String::from_utf8(quote_file_name(name).into_owned()).unwrap()
+        }
+
+        fn quoted_arg(arg: &str) -> String {
+            String::from_utf8(quote_shell_argument(arg.as_bytes()).into_owned()).unwrap()
+        }
+
+        #[test]
+        fn file_names() {
+            assert_eq!(quoted_name(b"src/main.rs"), "src/main.rs");
+            assert_eq!(quoted_name(b"why?*$'#~"), "why?*$'#~");
+            assert_eq!(quoted_name(b"two words"), r#""two words""#);
+            assert_eq!(quoted_name(b"say \"hi\""), r#""say \"hi\"""#);
+            if cfg!(windows) {
+                assert_eq!(quoted_name(b"C:\\temp"), r"C:\temp");
+                assert_eq!(quoted_name(b"C:\\my docs"), r#""C:\my docs""#);
+            } else {
+                assert_eq!(quoted_name(b"C:\\temp"), r#""C:\\temp""#);
+            }
+            assert_eq!(
+                quoted_name(b"\x07\x08\t\n\x0b\x0c\r"),
+                r#""\a\b\t\n\v\f\r""#
+            );
+            assert_eq!(quoted_name(b"\x1bx\x7f"), "\"\\033x\x7f\"");
+            assert_eq!(quoted_name("caf\u{e9}".as_bytes()), r#""caf\303\251""#);
+            assert_eq!(quoted_name(b"\xfe"), r#""\376""#);
+        }
+
+        #[test]
+        fn shell_arguments() {
+            assert_eq!(quoted_arg("-u"), "-u");
+            assert_eq!(quoted_arg("a,b:c@d%e+f{g}h]/i.j"), "a,b:c@d%e+f{g}h]/i.j");
+            assert_eq!(quoted_arg("x~#"), "x~#");
+            assert_eq!(quoted_arg("~x"), "'~x'");
+            assert_eq!(quoted_arg("#x"), "'#x'");
+            assert_eq!(quoted_arg("^fn (main|init)"), "'^fn (main|init)'");
+            assert_eq!(quoted_arg("--width=9"), "'--width=9'");
+            assert_eq!(quoted_arg(""), "''");
+            assert_eq!(quoted_arg("don't"), "\"don't\"");
+            assert_eq!(quoted_arg("don't $pay"), "'don'\\''t $pay'");
+        }
+    }
+
     mod write_line {
         use super::*;
         use pretty_assertions::assert_eq;
diff --git a/tests/by-util/test_diff.rs b/tests/by-util/test_diff.rs
index e142903..2b29278 100644
--- a/tests/by-util/test_diff.rs
+++ b/tests/by-util/test_diff.rs
@@ -797,3 +797,56 @@ fn function_lines() -> Result<(), Box<dyn std::error::Error>> {
         .stderr("'\\(': Unmatched ( or \\(\n");
     Ok(())
 }
+
+#[cfg(unix)]
+#[test]
+fn quoted_file_names() -> Result<(), Box<dyn std::error::Error>> {
+    let tmp_dir = tempdir()?;
+    let dir = tmp_dir.path().to_str().unwrap();
+    std::fs::write(tmp_dir.path().join("my notes"), "draft\n")?;
+    std::fs::write(tmp_dir.path().join("final\tv2"), "done\n")?;
+    std::fs::write(tmp_dir.path().join("plain$name"), "done\n")?;
+
+    let mut cmd = cargo_bin_cmd!("diffutils");
+    cmd.env("TZ", "UTC0")
+        .arg("diff")
+        .arg("-u")
+        .arg(format!("{dir}/my notes"))
+        .arg(format!("{dir}/final\tv2"));
+    cmd.assert()
+        .code(predicate::eq(1))
+        .stdout(predicate::str::is_match(format!(
+            "^--- \"{dir}/my notes\"\t[^\n]*\n\\+\\+\\+ \"{dir}/final\\\\tv2\"\t"
+        ))?);
+
+    // Names without special characters are left alone.
+    let mut cmd = cargo_bin_cmd!("diffutils");
+    cmd.arg("diff")
+        .arg("-c")
+        .arg(format!("{dir}/my notes"))
+        .arg(format!("{dir}/plain$name"));
+    cmd.assert()
+        .code(predicate::eq(1))
+        .stdout(predicate::str::contains(format!(
+            "\n--- {dir}/plain$name\t"
+        )));
+
+    // The diff -r header quotes the options for the shell and the names as
+    // in the other headers.
+    for (side, content) in [("one", "a\n"), ("two", "b\n")] {
+        std::fs::create_dir(tmp_dir.path().join(side))?;
+        std::fs::write(tmp_dir.path().join(side).join("my file"), content)?;
+    }
+    let mut cmd = cargo_bin_cmd!("diffutils");
+    cmd.current_dir(&tmp_dir)
+        .arg("diff")
+        .arg("-r")
+        .arg("-F")
+        .arg("my func")
+        .arg("one")
+        .arg("two");
+    cmd.assert()
+        .code(predicate::eq(1))
+        .stdout("diff -r -F 'my func' \"one/my file\" \"two/my file\"\n1c1\n< a\n---\n> b\n");
+    Ok(())
+}