diff --git a/man7/unix.7 b/man7/unix.7
index 3f41ad4cc..d04adb4f9 100644
--- a/man7/unix.7
+++ b/man7/unix.7
@@ -552,7 +552,8 @@ An in-flight file descriptor is one that has been sent using
 but has not yet been accepted in the recipient process using
 .BR recvmsg (2).
 
-This error is diagnosed since Linux 4.5.
+This error is diagnosed since mainline Linux 4.5
+(and in some earlier kernel versions where the fix has been backported).
 .\" commit 712f4aad406bb1ed67f3f98d04c044191f0ff593
 In earlier kernel versions,
 it was possible to place an unlimited number of file descriptors in flight,