diff --git a/contributors/people.toml b/contributors/people.toml
index 88e496fc7..43252507d 100644
--- a/contributors/people.toml
+++ b/contributors/people.toml
@@ -96,3 +96,6 @@ sync_github_name = true
 
 [people.tyrel]
 real_name = "Tyrel Haveman"
+
+[people.helenkwok]
+real_name = "Helen Kwok"
diff --git a/crates/xlsx/src/tables.rs b/crates/xlsx/src/tables.rs
index 141d8673a..23c936c4a 100644
--- a/crates/xlsx/src/tables.rs
+++ b/crates/xlsx/src/tables.rs
@@ -46,10 +46,11 @@ pub fn builtin_format(id: u32) -> Option<&'static str> {
     BUILTIN_FORMATS.iter().find(|(i, _)| *i == id).map(|(_, c)| *c)
 }
 
-/// Id to write for a format code when it is a locale-independent built-in (currency formats 5–8
-/// are written as custom formats because their meaning depends on the reader's locale).
+/// Id to write for a format code when it is a locale-independent built-in. The currency formats
+/// 5–8 and the accounting formats with a currency, 42 and 44, are written as custom formats because
+/// their meaning depends on the reader's locale.
 pub fn builtin_id(code: &str) -> Option<u32> {
-    BUILTIN_FORMATS.iter().find(|(i, c)| *c == code && !(5..=8).contains(i)).map(|(i, _)| *i)
+    BUILTIN_FORMATS.iter().find(|(i, c)| *c == code && !matches!(i, 5..=8 | 42 | 44)).map(|(i, _)| *i)
 }
 
 pub use gridcraft_core::color::INDEXED;
diff --git a/crates/xlsx/src/tests/locale_numfmt.rs b/crates/xlsx/src/tests/locale_numfmt.rs
new file mode 100644
index 000000000..3259a3657
--- /dev/null
+++ b/crates/xlsx/src/tests/locale_numfmt.rs
@@ -0,0 +1,61 @@
+//! Number formats whose meaning depends on the reader's locale are written with their code: the
+//! currency formats 5–8 and the accounting formats with a currency, 42 and 44. Written as a bare
+//! built-in id, LibreOffice and Excel in other locales show their own version (a 44 cell holding
+//! -0.14 reads `$ (0.14)` in US Excel but `- 0.14` in LibreOffice).
+
+use std::io::Read;
+use std::sync::Arc;
+
+use gridcraft_core::{CellRef, Value};
+use gridcraft_model::*;
+
+use crate::tables::builtin_format;
+use crate::{read_xlsx, write_xlsx};
+
+fn styles_xml(bytes: &[u8]) -> String {
+    let mut zip = zip::ZipArchive::new(std::io::Cursor::new(bytes)).unwrap();
+    let mut s = String::new();
+    zip.by_name("xl/styles.xml").unwrap().read_to_string(&mut s).unwrap();
+    s
+}
+
+/// Writes one cell formatted with `code`; returns the `numFmtId` its cell format points at, the
+/// `styles.xml` and the code read back.
+fn round_trip(code: &str) -> (u32, String, String) {
+    let mut wb = Workbook::new();
+    let style = wb.styles.derive(StyleId::DEFAULT, |s| s.num_fmt = NumFmt::new(code));
+    let mut sheet = Sheet::new("Sheet1");
+    sheet.cells.set(CellRef::new(0, 0), Cell { value: Value::Number(-0.14), formula: None, style });
+    wb.sheets = vec![Arc::new(sheet)];
+    let bytes = write_xlsx(&wb).unwrap();
+    let xml = styles_xml(&bytes);
+    let xfs = &xml[xml.find("<cellXfs").unwrap()..];
+    let id = xfs
+        .match_indices("numFmtId=\"")
+        .map(|(i, m)| xfs[i + m.len()..].split('"').next().unwrap().parse::<u32>().unwrap())
+        .find(|&id| id != 0)
+        .unwrap();
+    let (back, _) = read_xlsx(&bytes).unwrap();
+    let st = back.styles.get(back.sheet(0).unwrap().cell(CellRef::new(0, 0)).unwrap().style);
+    (id, xml, st.num_fmt.as_str().to_string())
+}
+
+#[test]
+fn currency_and_accounting_formats_are_written_with_their_code() {
+    for builtin in [5, 6, 7, 8, 42, 44] {
+        let code = builtin_format(builtin).unwrap();
+        let (id, xml, back) = round_trip(code);
+        assert!(id >= 164, "format {builtin} written as built-in id {id}");
+        assert!(xml.contains(&format!("<numFmt numFmtId=\"{id}\"")), "format {builtin}: no <numFmt> for id {id}");
+        assert_eq!(back, code, "format {builtin}");
+    }
+}
+
+#[test]
+fn locale_independent_built_ins_keep_their_id() {
+    for builtin in [3, 4, 10, 14, 41, 43, 49] {
+        let (id, _, back) = round_trip(builtin_format(builtin).unwrap());
+        assert_eq!(id, builtin);
+        assert_eq!(back, builtin_format(builtin).unwrap());
+    }
+}
diff --git a/crates/xlsx/src/tests/mod.rs b/crates/xlsx/src/tests/mod.rs
index c8f199a47..a7f6f1eb7 100644
--- a/crates/xlsx/src/tests/mod.rs
+++ b/crates/xlsx/src/tests/mod.rs
@@ -11,6 +11,7 @@ mod encrypted_tests;
 mod fixtures;
 mod ink_roundtrip;
 mod literal_category_roundtrip;
+mod locale_numfmt;
 mod malformed;
 mod multilevel_category_roundtrip;
 mod note_box;