1 files changed, 6 insertions, 1 deletions

diff --git a/lib/strftime.h b/lib/strftime.h
index e8501631573..fe0c4195a59 100644
--- a/lib/strftime.h
+++ b/lib/strftime.h
@@ -24,7 +24,12 @@ extern "C" {
 /* Just like strftime, but with two more arguments:
    POSIX requires that strftime use the local timezone information.
    Use the timezone __TZ instead.  Use __NS as the number of
-   nanoseconds in the %N directive.  */
+   nanoseconds in the %N directive.
+
+   On error, set errno and return 0.  Otherwise, return the number of
+   bytes generated (not counting the trailing NUL), preserving errno
+   if the number is 0.  This errno behavior is in draft POSIX 202x
+   plus some requested changes to POSIX.  */
 size_t nstrftime (char *restrict, size_t, char const *, struct tm const *,
                   timezone_t __tz, int __ns);