diff --git a/src/pkg/crypto/rc4/rc4_arm.s b/src/pkg/crypto/rc4/rc4_arm.s
index 3aad729406..b9ac72301c 100644
--- a/src/pkg/crypto/rc4/rc4_arm.s
+++ b/src/pkg/crypto/rc4/rc4_arm.s
@@ -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 !nacl
+
 #include "../../../cmd/ld/textflag.h"
 
 // Registers
diff --git a/src/pkg/crypto/rc4/rc4_asm.go b/src/pkg/crypto/rc4/rc4_asm.go
index fc71b9a6fa..02e5b67d55 100644
--- a/src/pkg/crypto/rc4/rc4_asm.go
+++ b/src/pkg/crypto/rc4/rc4_asm.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 amd64p32 arm 386
+// +build amd64 amd64p32 arm,!nacl 386
 
 package rc4
 
diff --git a/src/pkg/crypto/rc4/rc4_ref.go b/src/pkg/crypto/rc4/rc4_ref.go
index 1ecce1a7fb..e34bd34cf1 100644
--- a/src/pkg/crypto/rc4/rc4_ref.go
+++ b/src/pkg/crypto/rc4/rc4_ref.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,!amd64p32,!arm,!386
+// +build !amd64,!amd64p32,!arm,!386 arm,nacl
 
 package rc4