diff --git a/util/endian/big.go b/util/endian/big.go
new file mode 100644
index 000000000..0dcdbab1f
--- /dev/null
+++ b/util/endian/big.go
@@ -0,0 +1,10 @@
+// Copyright (c) 2020 Tailscale Inc & 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 mips mips64 ppc64 s390x
+
+package endian
+
+// Big is whether the current platform is big endian.
+const Big = true
diff --git a/util/endian/endian.go b/util/endian/endian.go
new file mode 100644
index 000000000..863ab638e
--- /dev/null
+++ b/util/endian/endian.go
@@ -0,0 +1,6 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package endian exports a constant about whether the machine is big endian.
+package endian
diff --git a/util/endian/little.go b/util/endian/little.go
new file mode 100644
index 000000000..dd8686356
--- /dev/null
+++ b/util/endian/little.go
@@ -0,0 +1,10 @@
+// Copyright (c) 2020 Tailscale Inc & 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 amd64 arm arm64 mips64le mipsle ppc64le riscv64 wasm
+
+package endian
+
+// Big is whether the current platform is big endian.
+const Big = false