diff --git a/ext/fileio/fileio.go b/ext/fileio/fileio.go
index 90c97272..dcb375ad 100644
--- a/ext/fileio/fileio.go
+++ b/ext/fileio/fileio.go
@@ -22,7 +22,7 @@ func Register(db *sqlite3.Conn) {
 // and the table-valued function fsdir;
 // fsys will be used to read files and list directories.
 func RegisterFS(db *sqlite3.Conn, fsys fs.FS) {
-	db.CreateFunction("lsmode", 1, 0, lsmode)
+	db.CreateFunction("lsmode", 1, sqlite3.DETERMINISTIC, lsmode)
 	db.CreateFunction("readfile", 1, sqlite3.DIRECTONLY, readfile(fsys))
 	if fsys == nil {
 		db.CreateFunction("writefile", -1, sqlite3.DIRECTONLY, writefile)
diff --git a/ext/zorder/zorder.go b/ext/zorder/zorder.go
new file mode 100644
index 00000000..8ab93724
--- /dev/null
+++ b/ext/zorder/zorder.go
@@ -0,0 +1,58 @@
+// Package zorder provides functions for z-order transformations.
+//
+// https://sqlite.org/src/doc/tip/ext/misc/zorder.c
+package zorder
+
+import (
+	"github.com/ncruces/go-sqlite3"
+	"github.com/ncruces/go-sqlite3/internal/util"
+)
+
+// Register registers the zorder and unzorder SQL functions.
+func Register(db *sqlite3.Conn) {
+	flags := sqlite3.DETERMINISTIC | sqlite3.INNOCUOUS
+	db.CreateFunction("zorder", -1, flags, zorder)
+	db.CreateFunction("unzorder", 3, flags, unzorder)
+}
+
+func zorder(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	var x [63]int64
+	for i := range arg {
+		x[i] = arg[i].Int64()
+	}
+	if len(arg) > len(x) {
+		ctx.ResultError(util.ErrorString("zorder: too many parameters"))
+		return
+	}
+
+	var z int64
+	if len(arg) > 0 {
+		for i := 0; i < 63; i++ {
+			j := i % len(arg)
+			z |= (x[j] & 1) << i
+			x[j] >>= 1
+		}
+	}
+
+	for i := range arg {
+		if x[i] != 0 {
+			ctx.ResultError(util.ErrorString("zorder: parameter too large"))
+			return
+		}
+	}
+	ctx.ResultInt64(z)
+}
+
+func unzorder(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	z := arg[0].Int64()
+	n := arg[1].Int64()
+	i := arg[2].Int64()
+
+	var k int
+	var x int64
+	for j := i; j < 63; j += n {
+		x |= ((z >> j) & 1) << k
+		k++
+	}
+	ctx.ResultInt64(x)
+}
diff --git a/ext/zorder/zorder_test.go b/ext/zorder/zorder_test.go
new file mode 100644
index 00000000..a2699ce8
--- /dev/null
+++ b/ext/zorder/zorder_test.go
@@ -0,0 +1,106 @@
+package zorder_test
+
+import (
+	"testing"
+
+	"github.com/ncruces/go-sqlite3"
+	"github.com/ncruces/go-sqlite3/driver"
+	_ "github.com/ncruces/go-sqlite3/embed"
+	"github.com/ncruces/go-sqlite3/ext/zorder"
+)
+
+func TestRegister_zorder(t *testing.T) {
+	t.Parallel()
+
+	db, err := driver.Open(":memory:", func(c *sqlite3.Conn) error {
+		zorder.Register(c)
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	var got int64
+	err = db.QueryRow(`SELECT zorder(2, 3)`).Scan(&got)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != 14 {
+		t.Errorf("got %d, want 14", got)
+	}
+
+	err = db.QueryRow(`SELECT zorder(4, 5)`).Scan(&got)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != 50 {
+		t.Errorf("got %d, want 14", got)
+	}
+
+	var check bool
+	err = db.QueryRow(`SELECT zorder(3, 4) BETWEEN zorder(2, 3) AND zorder(4, 5)`).Scan(&check)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !check {
+		t.Error("want true")
+	}
+
+	err = db.QueryRow(`SELECT zorder(2, 2) NOT BETWEEN zorder(2, 3) AND zorder(4, 5)`).Scan(&check)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !check {
+		t.Error("want true")
+	}
+}
+
+func TestRegister_unzorder(t *testing.T) {
+	t.Parallel()
+
+	db, err := driver.Open(":memory:", func(c *sqlite3.Conn) error {
+		zorder.Register(c)
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	var got int64
+	err = db.QueryRow(`SELECT unzorder(zorder(3, 4), 2, 0)`).Scan(&got)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != 3 {
+		t.Errorf("got %d, want 3", got)
+	}
+
+	err = db.QueryRow(`SELECT unzorder(zorder(3, 4), 2, 1)`).Scan(&got)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != 4 {
+		t.Errorf("got %d, want 4", got)
+	}
+}
+
+func TestRegister_error(t *testing.T) {
+	t.Parallel()
+
+	db, err := driver.Open(":memory:", func(c *sqlite3.Conn) error {
+		zorder.Register(c)
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	var got int64
+	err = db.QueryRow(`SELECT zorder(1, 2, 3, 100000)`).Scan(&got)
+	if err == nil {
+		t.Error("want error")
+	}
+}