diff --git a/argon2/blamka_amd64.go b/argon2/blamka_amd64.go
index 583ac4b..bb2b0d8 100644
--- a/argon2/blamka_amd64.go
+++ b/argon2/blamka_amd64.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 amd64,!gccgo,!appengine
+
 package argon2
 
 func init() {