diff --git a/newlib/libc/include/sys/features.h b/newlib/libc/include/sys/features.h
index 2900b332f..f28dd071b 100644
--- a/newlib/libc/include/sys/features.h
+++ b/newlib/libc/include/sys/features.h
@@ -425,7 +425,7 @@ extern "C" {
 #endif
 
 #define _POSIX_ADVISORY_INFO			200809L
-/* #define _POSIX_ASYNCHRONOUS_IO		    -1 */
+#define _POSIX_ASYNCHRONOUS_IO			200809L
 #define _POSIX_BARRIERS				200809L
 #define _POSIX_CHOWN_RESTRICTED			     1
 #define _POSIX_CLOCK_SELECTION			200809L
diff --git a/winsup/cygwin/sysconf.cc b/winsup/cygwin/sysconf.cc
index ff98f57a3..753febca4 100644
--- a/winsup/cygwin/sysconf.cc
+++ b/winsup/cygwin/sysconf.cc
@@ -528,7 +528,7 @@ static struct
   {cons, {c:SIGQUEUE_MAX}},		/*  18, _SC_SIGQUEUE_MAX */
   {cons, {c:TIMER_MAX}},		/*  19, _SC_TIMER_MAX */
   {nsup, {c:0}},			/*  20, _SC_TZNAME_MAX */
-  {cons, {c:-1L}},			/*  21, _SC_ASYNCHRONOUS_IO */
+  {cons, {c:_POSIX_ASYNCHRONOUS_IO}},	/*  21, _SC_ASYNCHRONOUS_IO */
   {cons, {c:_POSIX_FSYNC}},		/*  22, _SC_FSYNC */
   {cons, {c:_POSIX_MAPPED_FILES}},	/*  23, _SC_MAPPED_FILES */
   {cons, {c:-1L}},			/*  24, _SC_MEMLOCK */