diff --git a/man2/fcntl.2 b/man2/fcntl.2
index bd8feeb3b..b2d45cd9f 100644
--- a/man2/fcntl.2
+++ b/man2/fcntl.2
@@ -89,6 +89,17 @@ and we identify the argument using the name
 or
 .I void
 is specified if the argument is not required.
+
+Certain of the operations below are supported only since a particular
+Linux kernel version.
+The preferred method of checking whether the host kernel supports
+a particular operation is to invoke
+.BR fcntl ()
+with the desired
+.IR cmd
+value and then test whether the call failed with
+.BR EINVAL ,
+indicating that the kernel does not recognize this value.
 .SS Duplicating a file descriptor
 .TP
 .BR F_DUPFD " (\fIint\fP)"