diff --git a/man7/feature_test_macros.7 b/man7/feature_test_macros.7
index 08ac6fa8b..e6b9fba47 100644
--- a/man7/feature_test_macros.7
+++ b/man7/feature_test_macros.7
@@ -529,13 +529,19 @@ and
 .BR _SVID_SOURCE .
 .TP
 .B _REENTRANT
-Defining this macro exposes definitions of certain reentrant functions.
-For multithreaded programs, use
-.I "cc\ \-pthread"
-instead.
+Historically,
+defining this macro exposed definitions of certain reentrant functions.
+However, already for many years this macro has had few effects,
+and since glibc 2.3, no effects that were not also achieved by defining
+.BR _POSIX_C_SOURCE
+with a value of 199606L or greater.
+This macro is now deprecated; since glibc 2.25,
+defining it has the same effect as defining
+.BR _POSIX_C_SOURCE
+with a value of 199606L or greater.
 .TP
 .B _THREAD_SAFE
-Synonym for
+Synonym for the (deprecated)
 .BR _REENTRANT ,
 provided for compatibility with some other implementations.
 .TP