diff --git a/arm64/arm64spec/spec.go b/arm64/arm64spec/spec.go
index ee784e5..1000d01 100644
--- a/arm64/arm64spec/spec.go
+++ b/arm64/arm64spec/spec.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build go1.6,amd64 go1.8
+
 // arm64spec reads the ``ARMv8-A Reference Manual''
 // to collect instruction encoding details and writes those
 // details to standard output in JSON format.