diff --git a/go.mod b/go.mod
index 997071a..64042c9 100644
--- a/go.mod
+++ b/go.mod
@@ -5,5 +5,5 @@ go 1.12
 require (
 	golang.org/x/crypto v0.0.0-20190513172903-22d7a77e9e5f
 	golang.org/x/net v0.0.0-20190522155817-f3200d17e092
-	golang.org/x/sys v0.0.0-20190522044717-8097e1b27ff5
+	golang.org/x/sys v0.0.0-20190606203320-7fc4e5ec1444
 )
diff --git a/go.sum b/go.sum
index eea48be..c645ad2 100644
--- a/go.sum
+++ b/go.sum
@@ -6,6 +6,6 @@ golang.org/x/net v0.0.0-20190522155817-f3200d17e092 h1:4QSRKanuywn15aTZvI/mIDEgP
 golang.org/x/net v0.0.0-20190522155817-f3200d17e092/go.mod h1:HSz+uSET+XFnRR8LxR5pz3Of3rY3CfYBVs4xY44aLks=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20190522044717-8097e1b27ff5 h1:f005F/Jl5JLP036x7QIvUVhNTqxvSYwFIiyOh2q12iU=
-golang.org/x/sys v0.0.0-20190522044717-8097e1b27ff5/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190606203320-7fc4e5ec1444 h1:/d2cWp6PSamH4jDPFLyO150psQdqvtoNX8Zjg3AQ31g=
+golang.org/x/sys v0.0.0-20190606203320-7fc4e5ec1444/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
diff --git a/tun/wintun/guid/guid_windows.go b/tun/wintun/guid/guid_windows.go
deleted file mode 100644
index cc476d9..0000000
--- a/tun/wintun/guid/guid_windows.go
+++ /dev/null
@@ -1,41 +0,0 @@
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
- */
-
-package guid
-
-import (
-	"fmt"
-	"syscall"
-
-	"golang.org/x/sys/windows"
-)
-
-//sys	clsidFromString(lpsz *uint16, pclsid *windows.GUID) (err error) [failretval!=0] = ole32.CLSIDFromString
-
-//
-// FromString parses "{XXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}" string to GUID.
-//
-func FromString(str string) (*windows.GUID, error) {
-	strUTF16, err := syscall.UTF16PtrFromString(str)
-	if err != nil {
-		return nil, err
-	}
-	guid := &windows.GUID{}
-	err = clsidFromString(strUTF16, guid)
-	if err != nil {
-		return nil, err
-	}
-	return guid, nil
-}
-
-//
-// ToString function converts GUID to string
-// "{XXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}".
-//
-// The resulting string is uppercase.
-//
-func ToString(guid *windows.GUID) string {
-	return fmt.Sprintf("{%08X-%04X-%04X-%04X-%012X}", guid.Data1, guid.Data2, guid.Data3, guid.Data4[:2], guid.Data4[2:])
-}
diff --git a/tun/wintun/guid/mksyscall.go b/tun/wintun/guid/mksyscall.go
deleted file mode 100644
index 5c956cf..0000000
--- a/tun/wintun/guid/mksyscall.go
+++ /dev/null
@@ -1,8 +0,0 @@
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
- */
-
-package guid
-
-//go:generate go run $GOROOT/src/syscall/mksyscall_windows.go -output zguid_windows.go guid_windows.go
diff --git a/tun/wintun/guid/zguid_windows.go b/tun/wintun/guid/zguid_windows.go
deleted file mode 100644
index b0b4cce..0000000
--- a/tun/wintun/guid/zguid_windows.go
+++ /dev/null
@@ -1,55 +0,0 @@
-// Code generated by 'go generate'; DO NOT EDIT.
-
-package guid
-
-import (
-	"syscall"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-)
-
-var _ unsafe.Pointer
-
-// Do the interface allocations only once for common
-// Errno values.
-const (
-	errnoERROR_IO_PENDING = 997
-)
-
-var (
-	errERROR_IO_PENDING error = syscall.Errno(errnoERROR_IO_PENDING)
-)
-
-// errnoErr returns common boxed Errno values, to prevent
-// allocations at runtime.
-func errnoErr(e syscall.Errno) error {
-	switch e {
-	case 0:
-		return nil
-	case errnoERROR_IO_PENDING:
-		return errERROR_IO_PENDING
-	}
-	// TODO: add more here, after collecting data on the common
-	// error values see on Windows. (perhaps when running
-	// all.bat?)
-	return e
-}
-
-var (
-	modole32 = windows.NewLazySystemDLL("ole32.dll")
-
-	procCLSIDFromString = modole32.NewProc("CLSIDFromString")
-)
-
-func clsidFromString(lpsz *uint16, pclsid *windows.GUID) (err error) {
-	r1, _, e1 := syscall.Syscall(procCLSIDFromString.Addr(), 2, uintptr(unsafe.Pointer(lpsz)), uintptr(unsafe.Pointer(pclsid)), 0)
-	if r1 != 0 {
-		if e1 != 0 {
-			err = errnoErr(e1)
-		} else {
-			err = syscall.EINVAL
-		}
-	}
-	return
-}
diff --git a/tun/wintun/setupapi/setupapi_windows_test.go b/tun/wintun/setupapi/setupapi_windows_test.go
index a2edab8..b932d7d 100644
--- a/tun/wintun/setupapi/setupapi_windows_test.go
+++ b/tun/wintun/setupapi/setupapi_windows_test.go
@@ -11,7 +11,6 @@ import (
 	"testing"
 
 	"golang.org/x/sys/windows"
-	"golang.zx2c4.com/wireguard/tun/wintun/guid"
 )
 
 var deviceClassNetGUID = windows.GUID{Data1: 0x4d36e972, Data2: 0xe325, Data3: 0x11ce, Data4: [8]byte{0xbf, 0xc1, 0x08, 0x00, 0x2b, 0xe1, 0x03, 0x18}}
@@ -323,10 +322,10 @@ func TestSetupDiGetDeviceRegistryProperty(t *testing.T) {
 		} else if valStr, ok := val.(string); !ok {
 			t.Errorf("SetupDiGetDeviceRegistryProperty(SPDRP_CLASSGUID) should return string")
 		} else {
-			classGUID, err := guid.FromString(valStr)
+			classGUID, err := windows.GUIDFromString(valStr)
 			if err != nil {
 				t.Errorf("Error parsing GUID returned by SetupDiGetDeviceRegistryProperty(SPDRP_CLASSGUID): %s", err.Error())
-			} else if *classGUID != deviceClassNetGUID {
+			} else if classGUID != deviceClassNetGUID {
 				t.Errorf("SetupDiGetDeviceRegistryProperty(SPDRP_CLASSGUID) should return %x", deviceClassNetGUID)
 			}
 		}
diff --git a/tun/wintun/wintun_windows.go b/tun/wintun/wintun_windows.go
index 3d41f38..ac811af 100644
--- a/tun/wintun/wintun_windows.go
+++ b/tun/wintun/wintun_windows.go
@@ -15,7 +15,6 @@ import (
 	"golang.org/x/sys/windows"
 	"golang.org/x/sys/windows/registry"
 
-	"golang.zx2c4.com/wireguard/tun/wintun/guid"
 	"golang.zx2c4.com/wireguard/tun/wintun/netshell"
 	registryEx "golang.zx2c4.com/wireguard/tun/wintun/registry"
 	"golang.zx2c4.com/wireguard/tun/wintun/setupapi"
@@ -54,8 +53,8 @@ func makeWintun(deviceInfoSet setupapi.DevInfo, deviceInfoData *setupapi.DevInfo
 		return nil, fmt.Errorf("RegQueryStringValue(\"NetCfgInstanceId\") failed: %v", err)
 	}
 
-	// Convert to windows.GUID.
-	ifid, err := guid.FromString(valueStr)
+	// Convert to GUID.
+	ifid, err := windows.GUIDFromString(valueStr)
 	if err != nil {
 		return nil, fmt.Errorf("NetCfgInstanceId registry value is not a GUID (expected: \"{...}\", provided: %q)", valueStr)
 	}
@@ -73,7 +72,7 @@ func makeWintun(deviceInfoSet setupapi.DevInfo, deviceInfoData *setupapi.DevInfo
 	}
 
 	return &Wintun{
-		cfgInstanceID: *ifid,
+		cfgInstanceID: ifid,
 		luidIndex:     uint32(luidIdx),
 		ifType:        uint32(ifType),
 	}, nil
@@ -96,7 +95,7 @@ func GetInterface(ifname string, hwndParent uintptr) (*Wintun, error) {
 	// Create a list of network devices.
 	devInfoList, err := setupapi.SetupDiGetClassDevsEx(&deviceClassNetGUID, enumerator, hwndParent, setupapi.DIGCF_PRESENT, setupapi.DevInfo(0), machineName)
 	if err != nil {
-		return nil, fmt.Errorf("SetupDiGetClassDevsEx(%s) failed: %v", guid.ToString(&deviceClassNetGUID), err)
+		return nil, fmt.Errorf("SetupDiGetClassDevsEx(%v) failed: %v", deviceClassNetGUID, err)
 	}
 	defer devInfoList.Close()
 
@@ -189,14 +188,14 @@ func CreateInterface(description string, hwndParent uintptr) (*Wintun, bool, err
 	// Create an empty device info set for network adapter device class.
 	devInfoList, err := setupapi.SetupDiCreateDeviceInfoListEx(&deviceClassNetGUID, hwndParent, machineName)
 	if err != nil {
-		return nil, false, fmt.Errorf("SetupDiCreateDeviceInfoListEx(%s) failed: %v", guid.ToString(&deviceClassNetGUID), err)
+		return nil, false, fmt.Errorf("SetupDiCreateDeviceInfoListEx(%v) failed: %v", deviceClassNetGUID, err)
 	}
 	defer devInfoList.Close()
 
 	// Get the device class name from GUID.
 	className, err := setupapi.SetupDiClassNameFromGuidEx(&deviceClassNetGUID, machineName)
 	if err != nil {
-		return nil, false, fmt.Errorf("SetupDiClassNameFromGuidEx(%s) failed: %v", guid.ToString(&deviceClassNetGUID), err)
+		return nil, false, fmt.Errorf("SetupDiClassNameFromGuidEx(%v) failed: %v", deviceClassNetGUID, err)
 	}
 
 	// Create a new device info element and add it to the device info set.
@@ -516,14 +515,14 @@ func (wintun *Wintun) SetInterfaceName(ifname string) error {
 // netRegKeyName returns interface-specific network registry key name.
 //
 func (wintun *Wintun) netRegKeyName() string {
-	return fmt.Sprintf("SYSTEM\\CurrentControlSet\\Control\\Network\\%s\\%s\\Connection", guid.ToString(&deviceClassNetGUID), guid.ToString(&wintun.cfgInstanceID))
+	return fmt.Sprintf("SYSTEM\\CurrentControlSet\\Control\\Network\\%v\\%v\\Connection", deviceClassNetGUID, wintun.cfgInstanceID)
 }
 
 //
 // tcpipAdapterRegKeyName returns adapter-specific TCP/IP network registry key name.
 //
 func (wintun *Wintun) tcpipAdapterRegKeyName() string {
-	return fmt.Sprintf("SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Adapters\\%s", guid.ToString(&wintun.cfgInstanceID))
+	return fmt.Sprintf("SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Adapters\\%v", wintun.cfgInstanceID)
 }
 
 //
@@ -558,7 +557,7 @@ func (wintun *Wintun) deviceData(hwndParent uintptr) (setupapi.DevInfo, *setupap
 	// Create a list of network devices.
 	devInfoList, err := setupapi.SetupDiGetClassDevsEx(&deviceClassNetGUID, enumerator, hwndParent, setupapi.DIGCF_PRESENT, setupapi.DevInfo(0), machineName)
 	if err != nil {
-		return 0, nil, fmt.Errorf("SetupDiGetClassDevsEx(%s) failed: %v", guid.ToString(&deviceClassNetGUID), err.Error())
+		return 0, nil, fmt.Errorf("SetupDiGetClassDevsEx(%v) failed: %v", deviceClassNetGUID, err.Error())
 	}
 
 	// Iterate.