diff --git a/bytes/regexp.go b/bytes/regexp.go
index e810345..45a558a 100644
--- a/bytes/regexp.go
+++ b/bytes/regexp.go
@@ -1,14 +1,45 @@
 package bytes
 
 import (
+	"errors"
 	"fmt"
+	"io"
 	"regexp"
 	"strings"
+	"unicode/utf8"
 
 	"git.codemonkeysoftware.net/b/gigaparsec"
 	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
 )
 
+// RuneReader is an io.RuneReader backed by a Cursor, for compatibility
+// with the regexp package.
+type RuneReader struct {
+	cursor cursor.Cursor[byte]
+}
+
+func NewRuneReader(c cursor.Cursor[byte]) *RuneReader {
+	return &RuneReader{cursor: c}
+}
+
+func (rr *RuneReader) ReadRune() (r rune, size int, err error) {
+	var b [4]byte
+	s := b[:]
+	n, next, err := rr.cursor.Read(s)
+	if err != nil && !errors.Is(err, io.EOF) {
+		rr.cursor = next
+		return 0, 0, fmt.Errorf("ReadRune: %w", err)
+	}
+	s = s[:n]
+	r, size = utf8.DecodeRune(s)
+	rr.cursor = rr.cursor.At(rr.cursor.Pos() + uint64(size))
+	return r, size, err
+}
+
+func (rr *RuneReader) Cursor() cursor.Cursor[byte] {
+	return rr.cursor
+}
+
 func Regexp(str string) gigaparsec.Parser[byte, []byte] {
 	if !strings.HasPrefix(str, "^") {
 		str = "^" + str
@@ -16,7 +47,7 @@ func Regexp(str string) gigaparsec.Parser[byte, []byte] {
 	re := regexp.MustCompile(str)
 	expected := fmt.Sprintf("match `%s`", str)
 	return func(input gigaparsec.State[byte]) (consumed bool, result gigaparsec.Result[byte, []byte], err error) {
-		r := cursor.NewRuneReader(input.Cursor())
+		r := NewRuneReader(input.Cursor())
 		idx := re.FindReaderIndex(r)
 		// TODO Check error from r; this requires an Error() method on cursor.RuneReader.
 		if idx == nil {
diff --git a/bytes/regexp_test.go b/bytes/regexp_test.go
index fe1b656..d0d4583 100644
--- a/bytes/regexp_test.go
+++ b/bytes/regexp_test.go
@@ -9,3 +9,7 @@ func Todo(t *testing.T) {
 func TestRegexp(t *testing.T) {
 	Todo(t)
 }
+
+func TestRuneReader(t *testing.T) {
+	Todo(t)
+}
diff --git a/cursor/helper.go b/cursor/helper.go
index 1f0547d..715317c 100644
--- a/cursor/helper.go
+++ b/cursor/helper.go
@@ -1,10 +1,7 @@
 package cursor
 
 import (
-	"errors"
-	"fmt"
 	"io"
-	"unicode/utf8"
 )
 
 // BufferedReaderAt uses a buffer to supplement an io.Reader
@@ -25,31 +22,3 @@ func NewBufferedReaderAt(r io.Reader, minBuffer uint64) *BufferedReaderAt {
 func (b *BufferedReaderAt) ReadAt(dst []byte, offset int64) (int, error) {
 	return 0, nil
 }
-
-// RuneReader is an io.RuneReader backed by a Cursor, for compatibility
-// with the regexp package.
-type RuneReader struct {
-	cursor Cursor[byte]
-}
-
-func NewRuneReader(c Cursor[byte]) *RuneReader {
-	return &RuneReader{cursor: c}
-}
-
-func (rr *RuneReader) ReadRune() (r rune, size int, err error) {
-	var b [4]byte
-	s := b[:]
-	n, next, err := rr.cursor.Read(s)
-	if err != nil && !errors.Is(err, io.EOF) {
-		rr.cursor = next
-		return 0, 0, fmt.Errorf("ReadRune: %w", err)
-	}
-	s = s[:n]
-	r, size = utf8.DecodeRune(s)
-	rr.cursor = rr.cursor.At(rr.cursor.Pos() + uint64(size))
-	return r, size, err
-}
-
-func (rr *RuneReader) Cursor() Cursor[byte] {
-	return rr.cursor
-}