diff --git a/sha3/keccakf.go b/sha3/keccakf.go
index 13e7058..46d03ed 100644
--- a/sha3/keccakf.go
+++ b/sha3/keccakf.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 appengine gccgo
+
 package sha3
 
 // rc stores the round constants for use in the ι step.