diff --git a/chacha20poly1305/chacha20poly1305_amd64.go b/chacha20poly1305/chacha20poly1305_amd64.go
index f0d3485..4755033 100644
--- a/chacha20poly1305/chacha20poly1305_amd64.go
+++ b/chacha20poly1305/chacha20poly1305_amd64.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64,go1.7
+// +build go1.7,amd64,!gccgo,!appengine
 
 package chacha20poly1305
 
diff --git a/chacha20poly1305/chacha20poly1305_amd64.s b/chacha20poly1305/chacha20poly1305_amd64.s
index ac95844..f69cc91 100644
--- a/chacha20poly1305/chacha20poly1305_amd64.s
+++ b/chacha20poly1305/chacha20poly1305_amd64.s
@@ -4,7 +4,7 @@
 
 // This file was originally from https://golang.org/cl/24717 by Vlad Krasnov of CloudFlare.
 
-// +build go1.7
+// +build go1.7,amd64,!gccgo,!appengine
 
 #include "textflag.h"
 // General register allocation
diff --git a/chacha20poly1305/chacha20poly1305_noasm.go b/chacha20poly1305/chacha20poly1305_noasm.go
index 1d4dcd3..4c2eb70 100644
--- a/chacha20poly1305/chacha20poly1305_noasm.go
+++ b/chacha20poly1305/chacha20poly1305_noasm.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64 !go1.7
+// +build !amd64 !go1.7 gccgo appengine
 
 package chacha20poly1305