diff --git a/Doc/library/string.rst b/Doc/library/string.rst
index 9a13dc6..f5a1a3e 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -325,7 +325,7 @@
 The general form of a *standard format specifier* is:
 
 .. productionlist:: sf
-   format_spec: [[`fill`]`align`][`sign`][#][0][`width`][.`precision`][`type`]
+   format_spec: [[`fill`]`align`][`sign`][#][0][`width`][,][.`precision`][`type`]
    fill: <a character other than '}'>
    align: "<" | ">" | "=" | "^"
    sign: "+" | "-" | " "
@@ -383,6 +383,10 @@
 hexadecimal output.  If present, it specifies that the output will be prefixed
 by ``'0b'``, ``'0o'``, or ``'0x'``, respectively.
 
+The ``','`` option signals the use of a comma for a thousands separator.
+For a locale aware separator, use the ``'n'`` integer presentation type
+instead.
+
 *width* is a decimal integer defining the minimum field width.  If not
 specified, then the field width will be determined by the content.