diff --git a/README.md b/README.md
index 575751c..2f3254b 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,4 @@ these packages importable, but everything is otherwise unchanged.
 
 ## Re-extracting
 
-The `extract/` directory contains the code to do this. Run the Go program, then
-copy the contents of the `out/github.com/dependabot/gomodules-extracted`
-directory to the top level of this repo.
+Run `script/extract`.
diff --git a/cmd/go/_internal_/cfg/zdefaultcc.go b/cmd/go/_internal_/cfg/zdefaultcc.go
index 5f45a57..7297f75 100644
--- a/cmd/go/_internal_/cfg/zdefaultcc.go
+++ b/cmd/go/_internal_/cfg/zdefaultcc.go
@@ -7,10 +7,10 @@ const DefaultPkgConfig = `pkg-config`
 func DefaultCC(goos, goarch string) string {
 	switch goos + `/` + goarch {
 	}
-	return "gcc"
+	return "clang"
 }
 func DefaultCXX(goos, goarch string) string {
 	switch goos + `/` + goarch {
 	}
-	return "g++"
+	return "clang++"
 }
diff --git a/cmd/go/_internal_/robustio/robustio_darwin.go b/cmd/go/_internal_/robustio/robustio_darwin.go
new file mode 100644
index 0000000..99fd8eb
--- /dev/null
+++ b/cmd/go/_internal_/robustio/robustio_darwin.go
@@ -0,0 +1,21 @@
+// Copyright 2019 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.
+
+package robustio
+
+import (
+	"errors"
+	"syscall"
+)
+
+const errFileNotFound = syscall.ENOENT
+
+// isEphemeralError returns true if err may be resolved by waiting.
+func isEphemeralError(err error) bool {
+	var errno syscall.Errno
+	if errors.As(err, &errno) {
+		return errno == errFileNotFound
+	}
+	return false
+}
diff --git a/cmd/go/_internal_/robustio/robustio_flaky.go b/cmd/go/_internal_/robustio/robustio_flaky.go
new file mode 100644
index 0000000..3f0d75e
--- /dev/null
+++ b/cmd/go/_internal_/robustio/robustio_flaky.go
@@ -0,0 +1,92 @@
+// Copyright 2019 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 windows darwin
+
+package robustio
+
+import (
+	"errors"
+	"io/ioutil"
+	"math/rand"
+	"os"
+	"syscall"
+	"time"
+)
+
+const arbitraryTimeout = 2000 * time.Millisecond
+
+// retry retries ephemeral errors from f up to an arbitrary timeout
+// to work around filesystem flakiness on Windows and Darwin.
+func retry(f func() (err error, mayRetry bool)) error {
+	var (
+		bestErr		error
+		lowestErrno	syscall.Errno
+		start		time.Time
+		nextSleep	time.Duration	= 1 * time.Millisecond
+	)
+	for {
+		err, mayRetry := f()
+		if err == nil || !mayRetry {
+			return err
+		}
+
+		var errno syscall.Errno
+		if errors.As(err, &errno) && (lowestErrno == 0 || errno < lowestErrno) {
+			bestErr = err
+			lowestErrno = errno
+		} else if bestErr == nil {
+			bestErr = err
+		}
+
+		if start.IsZero() {
+			start = time.Now()
+		} else if d := time.Since(start) + nextSleep; d >= arbitraryTimeout {
+			break
+		}
+		time.Sleep(nextSleep)
+		nextSleep += time.Duration(rand.Int63n(int64(nextSleep)))
+	}
+
+	return bestErr
+}
+
+// rename is like os.Rename, but retries ephemeral errors.
+//
+// On Windows it wraps os.Rename, which (as of 2019-06-04) uses MoveFileEx with
+// MOVEFILE_REPLACE_EXISTING.
+//
+// Windows also provides a different system call, ReplaceFile,
+// that provides similar semantics, but perhaps preserves more metadata. (The
+// documentation on the differences between the two is very sparse.)
+//
+// Empirical error rates with MoveFileEx are lower under modest concurrency, so
+// for now we're sticking with what the os package already provides.
+func rename(oldpath, newpath string) (err error) {
+	return retry(func() (err error, mayRetry bool) {
+		err = os.Rename(oldpath, newpath)
+		return err, isEphemeralError(err)
+	})
+}
+
+// readFile is like ioutil.ReadFile, but retries ephemeral errors.
+func readFile(filename string) ([]byte, error) {
+	var b []byte
+	err := retry(func() (err error, mayRetry bool) {
+		b, err = ioutil.ReadFile(filename)
+
+		// Unlike in rename, we do not retry errFileNotFound here: it can occur
+		// as a spurious error, but the file may also genuinely not exist, so the
+		// increase in robustness is probably not worth the extra latency.
+		return err, isEphemeralError(err) && !errors.Is(err, errFileNotFound)
+	})
+	return b, err
+}
+
+func removeAll(path string) error {
+	return retry(func() (err error, mayRetry bool) {
+		err = os.RemoveAll(path)
+		return err, isEphemeralError(err)
+	})
+}
diff --git a/script/extract b/script/extract
new file mode 100755
index 0000000..dcd166e
--- /dev/null
+++ b/script/extract
@@ -0,0 +1,7 @@
+#!/bin/sh
+
+(cd extract && go run .) && rsync -rcv extract/out/github.com/dependabot/gomodules-extracted/* .
+
+curl -sL https://raw.githubusercontent.com/golang/go/master/LICENSE | tee _internal_/LICENSE > cmd/LICENSE
+git add _internal_ cmd
+