diff --git a/Misc/NEWS.d/next/Library/2025-01-29-14-30-54.gh-issue-129409.JZbOE6.rst b/Misc/NEWS.d/next/Library/2025-01-29-14-30-54.gh-issue-129409.JZbOE6.rst
new file mode 100644
index 00000000000000..7e00b44c0ef471
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-01-29-14-30-54.gh-issue-129409.JZbOE6.rst
@@ -0,0 +1,2 @@
+Fix an integer overflow in the :mod:`csv` module when writing a data field
+larger than 2GB.
diff --git a/Modules/_csv.c b/Modules/_csv.c
index 9a7b7d27c2ed39..df7207d0894af8 100644
--- a/Modules/_csv.c
+++ b/Modules/_csv.c
@@ -1074,7 +1074,7 @@ join_append_data(WriterObj *self, int field_kind, const void *field_data,
                  int copy_phase)
 {
     DialectObj *dialect = self->dialect;
-    int i;
+    Py_ssize_t i;
     Py_ssize_t rec_len;
 
 #define INCLEN \