--- Libc/Libc-583/stdio/mktemp.3
+++ Libc/Libc-498/stdio/mktemp.3
@@ -232,6 +232,13 @@
 This will ensure that the program does not continue blindly
 in the event that an attacker has already created the file
 with the intention of manipulating or reading its contents.
+.Pp
+The implementation of these functions calls
+.Xr arc4random 3 ,
+which is not reentrant.
+You must provide your own locking around this and other consumers of the
+.Xr arc4random 3
+API.
 .Sh LEGACY SYNOPSIS
 .Fd #include <unistd.h>
 .Pp