diff --git a/src/runtime/internal/sys/intrinsics.go b/src/runtime/internal/sys/intrinsics.go
index 1054c6948f403..08a062f85acf3 100644
--- a/src/runtime/internal/sys/intrinsics.go
+++ b/src/runtime/internal/sys/intrinsics.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 !386
+
 package sys
 
 // Using techniques from http://supertech.csail.mit.edu/papers/debruijn.pdf
diff --git a/src/runtime/internal/sys/intrinsics_386.s b/src/runtime/internal/sys/intrinsics_386.s
new file mode 100644
index 0000000000000..1f48e264922fa
--- /dev/null
+++ b/src/runtime/internal/sys/intrinsics_386.s
@@ -0,0 +1,68 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "textflag.h"
+
+TEXT runtime∕internal∕sys·Ctz64(SB), NOSPLIT, $0-16
+	MOVL	$0, ret_hi+12(FP)
+
+	// Try low 32 bits.
+	MOVL	x_lo+0(FP), AX
+	BSFL	AX, AX
+	JZ	tryhigh
+	MOVL	AX, ret_lo+8(FP)
+	RET
+
+tryhigh:
+	// Try high 32 bits.
+	MOVL	x_hi+4(FP), AX
+	BSFL	AX, AX
+	JZ	none
+	ADDL	$32, AX
+	MOVL	AX, ret_lo+8(FP)
+	RET
+
+none:
+	// No bits are set.
+	MOVL	$64, ret_lo+8(FP)
+	RET
+
+TEXT runtime∕internal∕sys·Ctz32(SB), NOSPLIT, $0-8
+	MOVL	x+0(FP), AX
+	BSFL	AX, AX
+	JNZ	2(PC)
+	MOVL	$32, AX
+	MOVL	AX, ret+4(FP)
+	RET
+
+TEXT runtime∕internal∕sys·Ctz16(SB), NOSPLIT, $0-6
+	MOVW	x+0(FP), AX
+	BSFW	AX, AX
+	JNZ	2(PC)
+	MOVW	$16, AX
+	MOVW	AX, ret+4(FP)
+	RET
+
+TEXT runtime∕internal∕sys·Ctz8(SB), NOSPLIT, $0-5
+	MOVBLZX	x+0(FP), AX
+	BSFL	AX, AX
+	JNZ	2(PC)
+	MOVB	$8, AX
+	MOVB	AX, ret+4(FP)
+	RET
+
+TEXT runtime∕internal∕sys·Bswap64(SB), NOSPLIT, $0-16
+	MOVL	x_lo+0(FP), AX
+	MOVL	x_hi+4(FP), BX
+	BSWAPL	AX
+	BSWAPL	BX
+	MOVL	BX, ret_lo+8(FP)
+	MOVL	AX, ret_hi+12(FP)
+	RET
+
+TEXT runtime∕internal∕sys·Bswap32(SB), NOSPLIT, $0-8
+	MOVL	x+0(FP), AX
+	BSWAPL	AX
+	MOVL	AX, ret+4(FP)
+	RET
diff --git a/src/runtime/internal/sys/intrinsics_stubs.go b/src/runtime/internal/sys/intrinsics_stubs.go
new file mode 100644
index 0000000000000..079844fda4ea5
--- /dev/null
+++ b/src/runtime/internal/sys/intrinsics_stubs.go
@@ -0,0 +1,14 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build 386
+
+package sys
+
+func Ctz64(x uint64) uint64
+func Ctz32(x uint32) uint32
+func Ctz16(x uint16) uint16
+func Ctz8(x uint8) uint8
+func Bswap64(x uint64) uint64
+func Bswap32(x uint32) uint32