diff --git a/helper/iofs/iofs.go b/helper/iofs/iofs.go
new file mode 100644
index 0000000..be8f348
--- /dev/null
+++ b/helper/iofs/iofs.go
@@ -0,0 +1,140 @@
+// Package iofs provides an adapter from billy.Filesystem to a the
+// standard library io.fs.FS interface.
+package iofs
+
+import (
+	"io"
+	"io/fs"
+	"path/filepath"
+
+	billyfs "github.com/go-git/go-billy/v5"
+	"github.com/go-git/go-billy/v5/helper/polyfill"
+)
+
+// Wrap adapts a billy.Filesystem to a io.fs.FS.
+func New(fs billyfs.Basic) fs.FS {
+	return &adapterFs{fs: polyfill.New(fs)}
+}
+
+type adapterFs struct {
+	fs billyfs.Filesystem
+}
+
+// Type assertion that adapterFS implements the following interfaces:
+var _ fs.FS = (*adapterFs)(nil)
+var _ fs.ReadDirFS = (*adapterFs)(nil)
+var _ fs.StatFS = (*adapterFs)(nil)
+var _ fs.ReadFileFS = (*adapterFs)(nil)
+
+// TODO: implement fs.GlobFS, which will be a fair bit more code.
+
+// Open opens the named file on the underlying FS, implementing fs.FS (returning a file or error).
+func (a *adapterFs) Open(name string) (fs.File, error) {
+	if name[0] == '/' || name != filepath.Clean(name) {
+		// fstest.TestFS explicitly checks that these should return error.
+		// MemFS performs the clean internally, so we need to block that here for testing purposes.
+		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrInvalid}
+	}
+	stat, err := a.fs.Stat(name)
+	if err != nil {
+		return nil, err
+	}
+	if stat.IsDir() {
+		entries, err := a.ReadDir(name)
+		if err != nil {
+			return nil, err
+		}
+		return makeDir(stat, entries), nil
+	}
+	file, err := a.fs.Open(name)
+	return &adapterFile{file: file, info: stat}, err
+}
+
+// ReadDir reads the named directory, implementing fs.ReadDirFS (returning a listing or error).
+func (a *adapterFs) ReadDir(name string) ([]fs.DirEntry, error) {
+	items, err := a.fs.ReadDir(name)
+	if err != nil {
+		return nil, err
+	}
+	entries := make([]fs.DirEntry, len(items))
+	for i, item := range items {
+		entries[i] = fs.FileInfoToDirEntry(item)
+	}
+	return entries, nil
+}
+
+// Stat returns information on the named file, implementing fs.StatFS (returning FileInfo or error).
+func (a *adapterFs) Stat(name string) (fs.FileInfo, error) {
+	return a.fs.Stat(name)
+}
+
+// ReadFile reads the named file and returns its contents, implementing fs.ReadFileFS (returning contents or error).
+func (a *adapterFs) ReadFile(name string) ([]byte, error) {
+	stat, err := a.fs.Stat(name)
+	if err != nil {
+		return nil, err
+	}
+	b := make([]byte, stat.Size())
+	file, err := a.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	_, err = file.Read(b)
+	return b, err
+}
+
+type adapterFile struct {
+	file billyfs.File
+	info fs.FileInfo
+}
+
+var _ fs.File = (*adapterFile)(nil)
+
+// Close closes the file, implementing fs.File (and io.Closer).
+func (a *adapterFile) Close() error {
+	return a.file.Close()
+}
+
+// Read reads bytes from the file, implementing fs.File (and io.Reader).
+func (a *adapterFile) Read(b []byte) (int, error) {
+	return a.file.Read(b)
+}
+
+// Stat returns file information, implementing fs.File (returning FileInfo or error).
+func (a *adapterFile) Stat() (fs.FileInfo, error) {
+	return a.info, nil
+}
+
+type adapterDirFile struct {
+	adapterFile
+	entries []fs.DirEntry
+}
+
+var _ fs.ReadDirFile = (*adapterDirFile)(nil)
+
+func makeDir(stat fs.FileInfo, entries []fs.DirEntry) *adapterDirFile {
+	return &adapterDirFile{
+		adapterFile: adapterFile{info: stat},
+		entries:     entries,
+	}
+}
+
+// Close closes the directory, implementing fs.File (and io.Closer).
+// Subtle: note that this is shadowing adapterFile.Close.
+func (a *adapterDirFile) Close() error {
+	return nil
+}
+
+// ReadDir reads the directory contents, implementing fs.ReadDirFile (returning directory listing or error).
+func (a *adapterDirFile) ReadDir(n int) ([]fs.DirEntry, error) {
+	if len(a.entries) == 0 && n > 0 {
+		return nil, io.EOF
+	}
+	if n <= 0 || n > len(a.entries) {
+		n = len(a.entries)
+	}
+	entries := a.entries[:n]
+	a.entries = a.entries[n:]
+	return entries, nil
+}
diff --git a/helper/iofs/iofs_test.go b/helper/iofs/iofs_test.go
new file mode 100644
index 0000000..02d25de
--- /dev/null
+++ b/helper/iofs/iofs_test.go
@@ -0,0 +1,156 @@
+package iofs
+
+import (
+	"errors"
+	"io/fs"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"testing/fstest"
+
+	billyfs "github.com/go-git/go-billy/v5"
+	"github.com/go-git/go-billy/v5/memfs"
+)
+
+type errorList interface {
+	Unwrap() []error
+}
+
+type wrappedError interface {
+	Unwrap() error
+}
+
+// TestWithFSTest leverages the packaged Go fstest package, which seems comprehensive.
+func TestWithFSTest(t *testing.T) {
+	t.Parallel()
+	memfs := memfs.New()
+	iofs := New(memfs)
+
+	files := map[string]string{
+		"foo.txt":                       "hello, world",
+		"bar.txt":                       "goodbye, world",
+		filepath.Join("dir", "baz.txt"): "こんにちわ, world",
+	}
+	created_files := make([]string, 0, len(files))
+	for filename, contents := range files {
+		makeFile(memfs, t, filename, contents)
+		created_files = append(created_files, filename)
+	}
+
+	if runtime.GOOS == "windows" {
+		t.Skip("fstest.TestFS is not yet windows path aware")
+	}
+
+	err := fstest.TestFS(iofs, created_files...)
+	if err != nil {
+		checkFsTestError(t, err, files)
+	}
+}
+
+func TestDeletes(t *testing.T) {
+	t.Parallel()
+	memfs := memfs.New()
+	iofs := New(memfs).(fs.ReadFileFS)
+
+	makeFile(memfs, t, "foo.txt", "hello, world")
+	makeFile(memfs, t, "deleted", "nothing to see")
+
+	if _, err := iofs.ReadFile("nonexistent"); err == nil {
+		t.Errorf("expected error for nonexistent file")
+	}
+
+	data, err := iofs.ReadFile("deleted")
+	if err != nil {
+		t.Fatalf("failed to read file before delete: %v", err)
+	}
+	if string(data) != "nothing to see" {
+		t.Errorf("unexpected contents before delete: %v", data)
+	}
+
+	if err := memfs.Remove("deleted"); err != nil {
+		t.Fatalf("failed to remove file: %v", err)
+	}
+
+	if _, err = iofs.ReadFile("deleted"); err == nil {
+		t.Errorf("file existed after delete!")
+	}
+}
+
+func makeFile(fs billyfs.Basic, t *testing.T, filename string, contents string) {
+	t.Helper()
+	file, err := fs.Create(filename)
+	if err != nil {
+		t.Fatalf("failed to create file %s: %v", filename, err)
+	}
+	defer file.Close()
+	_, err = file.Write([]byte(contents))
+	if err != nil {
+		t.Fatalf("failed to write to file %s: %v", filename, err)
+	}
+}
+
+func checkFsTestError(t *testing.T, err error, files map[string]string) {
+	t.Helper()
+
+	if unwrapped := errors.Unwrap(err); unwrapped != nil {
+		err = unwrapped
+	}
+
+	// Go >= 1.23 (after https://cs.opensource.google/go/go/+/74cce866f865c3188a34309e4ebc7a5c9ed0683d)
+	// has nicely-Joined wrapped errors.  Try that first.
+	if errs, ok := err.(errorList); ok {
+		for _, e := range errs.Unwrap() {
+
+			if strings.Contains(e.Error(), "ModTime") {
+				// Memfs returns the current time for Stat().ModTime(), which triggers
+				// a diff complaint in fstest.  We can ignore this, or store modtimes
+				// for every file in Memfs (at a cost of 16 bytes / file).
+				t.Log("Skipping ModTime error (ok).")
+			} else {
+				t.Errorf("Unexpected fstest error: %v", e)
+			}
+		}
+	} else {
+		if runtime.Version() >= "go1.23" {
+			t.Fatalf("Failed to test fs:\n%v", err)
+		}
+		// filter lines from the error text corresponding to the above errors;
+		// output looks like:
+		// TestFS found errors:
+		//         bar.txt: mismatch:
+		//		entry.Info() = bar.txt IsDir=false Mode=-rw-rw-rw- Size=14 ModTime=2024-09-17 10:09:00.377023639 +0000 UTC m=+0.002625548
+		//		file.Stat() = bar.txt IsDir=false Mode=-rw-rw-rw- Size=14 ModTime=2024-09-17 10:09:00.376907011 +0000 UTC m=+0.002508970
+		//
+		//	bar.txt: fs.Stat(...) = bar.txt IsDir=false Mode=-rw-rw-rw- Size=14 ModTime=2024-09-17 10:09:00.381356651 +0000 UTC m=+0.006959191
+		//		want bar.txt IsDir=false Mode=-rw-rw-rw- Size=14 ModTime=2024-09-17 10:09:00.376907011 +0000 UTC m=+0.002508970
+		//	bar.txt: fsys.Stat(...) = bar.txt IsDir=false Mode=-rw-rw-rw- Size=14 ModTime=2024-09-17 10:09:00.381488617 +0000 UTC m=+0.007090346
+		//		want bar.txt IsDir=false Mode=-rw-rw-rw- Size=14 ModTime=2024-09-17 10:09:00.376907011 +0000 UTC m=+0.002508970
+		// We filter on "empty line" or "ModTime" or "$filename: mismatch" to ignore these.
+		lines := strings.Split(err.Error(), "\n")
+		filtered := make([]string, 0, len(lines))
+		filename_mismatches := make(map[string]struct{}, len(files)*2)
+		for name := range files {
+			for dirname := name; dirname != "."; dirname = filepath.Dir(dirname) {
+				filename_mismatches[dirname+": mismatch:"] = struct{}{}
+			}
+		}
+		if strings.TrimSpace(lines[0]) == "TestFS found errors:" {
+			lines = lines[1:]
+		}
+		for _, line := range lines {
+			trimmed := strings.TrimSpace(line)
+			if trimmed == "" || strings.Contains(trimmed, "ModTime=") {
+				continue
+			}
+
+			if _, ok := filename_mismatches[trimmed]; ok {
+				continue
+			}
+			filtered = append(filtered, line)
+		}
+		if len(filtered) > 0 {
+			t.Fatalf("Failed to test fs:\n%s", strings.Join(filtered, "\n"))
+		}
+	}
+}