diff --git a/vendor/golang.org/x/sys/unix/syscall.go b/vendor/golang.org/x/sys/unix/syscall.go
index fd4ee8e..0d4b1d7 100644
--- a/vendor/golang.org/x/sys/unix/syscall.go
+++ b/vendor/golang.org/x/sys/unix/syscall.go
@@ -50,4 +50,5 @@
 }
 
 // Single-word zero for use when we need a valid pointer to 0 bytes.
+// See mkunix.pl.
 var _zero uintptr