diff --git a/unix/syscall_darwin.go b/unix/syscall_darwin.go
index 0cf31ac..e2a05ee 100644
--- a/unix/syscall_darwin.go
+++ b/unix/syscall_darwin.go
@@ -49,6 +49,11 @@
 	raw    RawSockaddrDatalink
 }
 
+// Some external packages rely on SYS___SYSCTL being defined to implement their
+// own sysctl wrappers. Provide it here, even though direct syscalls are no
+// longer supported on darwin.
+const SYS___SYSCTL = 202
+
 // Translate "kern.hostname" to []_C_int{0,1,2,3}.
 func nametomib(name string) (mib []_C_int, err error) {
 	const siz = unsafe.Sizeof(mib[0])