diff --git a/pkg/driverutil/disk.go b/pkg/driverutil/disk.go
index a9ab18ef311..17c7496dcfb 100644
--- a/pkg/driverutil/disk.go
+++ b/pkg/driverutil/disk.go
@@ -38,23 +38,23 @@ func EnsureDisk(ctx context.Context, instDir, diskSize string, diskImageFormat i
 	if err != nil {
 		return err
 	}
+	destDisk := baseDisk
 	if isBaseDiskISO {
-		// Create an empty data volume (sparse)
+		destDisk = diffDisk
+
+		// Create an empty data volume for the diff disk
 		diffDiskF, err := os.Create(diffDisk)
 		if err != nil {
 			return err
 		}
 
-		err = diskUtil.MakeSparse(ctx, diffDiskF, 0)
-		if err != nil {
-			diffDiskF.Close()
-			return fmt.Errorf("failed to create sparse diff disk %q: %w", diffDisk, err)
+		if err = diffDiskF.Close(); err != nil {
+			return err
 		}
-		return diffDiskF.Close()
 	}
 	// Check whether to use ASIF format
 
-	if err = diskUtil.Convert(ctx, diskImageFormat, baseDisk, diffDisk, &diskSizeInBytes, false); err != nil {
+	if err = diskUtil.Convert(ctx, diskImageFormat, destDisk, diffDisk, &diskSizeInBytes, false); err != nil {
 		return fmt.Errorf("failed to convert %q to a disk %q: %w", baseDisk, diffDisk, err)
 	}
 	return err
diff --git a/pkg/driverutil/disk_test.go b/pkg/driverutil/disk_test.go
new file mode 100644
index 00000000000..583feb19c62
--- /dev/null
+++ b/pkg/driverutil/disk_test.go
@@ -0,0 +1,150 @@
+// SPDX-FileCopyrightText: Copyright The Lima Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package driverutil
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/lima-vm/go-qcow2reader"
+	"github.com/lima-vm/go-qcow2reader/image"
+	"gotest.tools/v3/assert"
+
+	"github.com/lima-vm/lima/v2/pkg/iso9660util"
+	"github.com/lima-vm/lima/v2/pkg/limatype/filenames"
+	"github.com/lima-vm/lima/v2/pkg/osutil"
+)
+
+const (
+	typeRAW  = image.Type("raw")
+	typeASIF = image.Type("asif")
+)
+
+func writeMinimalISO(t *testing.T, path string) {
+	t.Helper()
+	entries := []iso9660util.Entry{
+		{Path: "/hello.txt", Reader: strings.NewReader("hello world")},
+	}
+	assert.NilError(t, iso9660util.Write(path, "TESTISO", entries))
+}
+
+func writeNonISO(t *testing.T, path string) {
+	t.Helper()
+	size := 64 * 1024
+	buf := make([]byte, size)
+	copy(buf[0x8001:], "XXXXX")
+	assert.NilError(t, os.WriteFile(path, buf, 0o644))
+}
+
+func sha256File(t *testing.T, path string) string {
+	t.Helper()
+	b, err := os.ReadFile(path)
+	assert.NilError(t, err)
+	sum := sha256.Sum256(b)
+	return hex.EncodeToString(sum[:])
+}
+
+func detectImageType(t *testing.T, path string) image.Type {
+	t.Helper()
+	f, err := os.Open(path)
+	assert.NilError(t, err)
+	defer f.Close()
+	img, err := qcow2reader.Open(f)
+	assert.NilError(t, err)
+	return img.Type()
+}
+
+func checkDisk(t *testing.T, diff string, expectedType image.Type) {
+	t.Helper()
+	fi, err := os.Stat(diff)
+	assert.NilError(t, err)
+	assert.Assert(t, fi.Size() > 0)
+	assert.Equal(t, detectImageType(t, diff), expectedType)
+}
+
+func isMacOS26OrHigher() bool {
+	if runtime.GOOS != "darwin" {
+		return false
+	}
+	version, err := osutil.ProductVersion()
+	if err != nil {
+		return false
+	}
+	return version.Major >= 26
+}
+
+func TestEnsureDisk_WithISOBaseImage(t *testing.T) {
+	instDir := t.TempDir()
+	base := filepath.Join(instDir, filenames.BaseDisk)
+	diff := filepath.Join(instDir, filenames.DiffDisk)
+
+	writeMinimalISO(t, base)
+	isISO, err := iso9660util.IsISO9660(base)
+	assert.NilError(t, err)
+	assert.Assert(t, isISO)
+	baseHashBefore := sha256File(t, base)
+
+	formats := []image.Type{typeRAW}
+	if isMacOS26OrHigher() {
+		formats = append(formats, typeASIF)
+	}
+
+	for _, format := range formats {
+		assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", format))
+		isISO, err = iso9660util.IsISO9660(base)
+		assert.NilError(t, err)
+		assert.Assert(t, isISO)
+		assert.Equal(t, baseHashBefore, sha256File(t, base))
+		checkDisk(t, diff, format)
+		assert.NilError(t, os.Remove(diff))
+	}
+}
+
+func TestEnsureDisk_WithNonISOBaseImage(t *testing.T) {
+	instDir := t.TempDir()
+	base := filepath.Join(instDir, filenames.BaseDisk)
+	diff := filepath.Join(instDir, filenames.DiffDisk)
+
+	writeNonISO(t, base)
+	isISO, err := iso9660util.IsISO9660(base)
+	assert.NilError(t, err)
+	assert.Assert(t, !isISO)
+
+	formats := []image.Type{typeRAW}
+	if isMacOS26OrHigher() {
+		formats = append(formats, typeASIF)
+	}
+
+	for _, format := range formats {
+		assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", format))
+		checkDisk(t, diff, format)
+		assert.NilError(t, os.Remove(diff))
+	}
+}
+
+func TestEnsureDisk_ExistingDiffDisk(t *testing.T) {
+	instDir := t.TempDir()
+	base := filepath.Join(instDir, filenames.BaseDisk)
+	diff := filepath.Join(instDir, filenames.DiffDisk)
+
+	writeNonISO(t, base)
+
+	formats := []image.Type{typeRAW}
+	if isMacOS26OrHigher() {
+		formats = append(formats, typeASIF)
+	}
+
+	for _, format := range formats {
+		assert.NilError(t, os.WriteFile(diff, []byte("preexisting"), 0o644))
+		origHash := sha256File(t, diff)
+		assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", format))
+		assert.Equal(t, sha256File(t, diff), origHash)
+		assert.NilError(t, os.Remove(diff))
+	}
+}
diff --git a/pkg/imgutil/nativeimgutil/nativeimgutil.go b/pkg/imgutil/nativeimgutil/nativeimgutil.go
index 59e45c15267..e0c74830bdc 100644
--- a/pkg/imgutil/nativeimgutil/nativeimgutil.go
+++ b/pkg/imgutil/nativeimgutil/nativeimgutil.go
@@ -62,10 +62,10 @@ func convertTo(destType image.Type, source, dest string, size *int64, allowSourc
 	logrus.Infof("Converting %q (%s) to a %s disk %q", source, srcImg.Type(), destType, dest)
 	switch t := srcImg.Type(); t {
 	case raw.Type:
-		if err = srcF.Close(); err != nil {
-			return err
-		}
 		if destType == raw.Type {
+			if err = srcF.Close(); err != nil {
+				return err
+			}
 			return convertRawToRaw(source, dest, size)
 		}
 	case qcow2.Type: