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diff --git a/lib/vasnprintf.c b/lib/vasnprintf.c
index fecaf27..2e4eb19 100644
--- a/lib/vasnprintf.c
+++ b/lib/vasnprintf.c
@@ -4869,10 +4869,9 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
#endif
*fbp = dp->conversion;
#if USE_SNPRINTF
-# if ! (((__GLIBC__ > 2 \
- || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3)) \
- && !defined __UCLIBC__) \
- || (defined __APPLE__ && defined __MACH__) \
+# if ! (((__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3)) \
+ && !defined __UCLIBC__) \
+ || (defined __APPLE__ && defined __MACH__) \
|| ((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__))
fbp[1] = '%';
fbp[2] = 'n';
@@ -4887,9 +4886,13 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
in format strings in writable memory may crash the program
(if compiled with _FORTIFY_SOURCE=2), so we should avoid it
in this situation. */
- /* macOS 10.13 High Sierra behaves like glibc with
- _FORTIFY_SOURCE=2, and older macOS releases
- presumably do not need %n. */
+ /* On Mac OS X 10.3 or newer, we know that snprintf's return
+ value conforms to ISO C 99: the tests gl_SNPRINTF_RETVAL_C99
+ and gl_SNPRINTF_TRUNCATION_C99 pass.
+ Therefore we can avoid using %n in this situation.
+ On Mac OS X 10.13 or newer, the use of %n in format strings
+ in writable memory by default crashes the program, so we
+ should avoid it in this situation. */
/* On native Windows systems (such as mingw), we can avoid using
%n because:
- Although the gl_SNPRINTF_TRUNCATION_C99 test fails,
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