prefer_openssl: add amd64 constraint

Optimized assembly versions for Go GCM are only available
on amd64.

1 files changed, 4 insertions, 3 deletions

diff --git a/internal/prefer_openssl/prefer_go1.5.go b/internal/prefer_openssl/prefer_go1.5.go
index 4b681e7..51a07ab 100644
--- a/internal/prefer_openssl/prefer_go1.5.go
+++ b/internal/prefer_openssl/prefer_go1.5.go
@@ -1,9 +1,10 @@
-// +build !go1.6
-// = go 1.5 or lower
+// +build !go1.6 !amd64
+// not go1.6+ OR not amd64
 
 package prefer_openssl
 
 func PreferOpenSSL() bool {
-	// OpenSSL is always faster than Go GCM on old Go versions.
+	// OpenSSL is always faster than Go GCM on old Go versions or on anything
+	// other than amd64
 	return true
 }