diff --git a/pkg/osbuild/mount.go b/pkg/osbuild/mount.go
index 5b9e730387..96a44ae00c 100644
--- a/pkg/osbuild/mount.go
+++ b/pkg/osbuild/mount.go
@@ -1,11 +1,12 @@
 package osbuild
 
 type Mount struct {
-	Name    string       `json:"name"`
-	Type    string       `json:"type"`
-	Source  string       `json:"source,omitempty"`
-	Target  string       `json:"target,omitempty"`
-	Options MountOptions `json:"options,omitempty"`
+	Name      string       `json:"name"`
+	Type      string       `json:"type"`
+	Source    string       `json:"source,omitempty"`
+	Target    string       `json:"target,omitempty"`
+	Options   MountOptions `json:"options,omitempty"`
+	Partition *int         `json:"partition,omitempty"`
 }
 
 type MountOptions interface {
diff --git a/pkg/osbuild/mount_test.go b/pkg/osbuild/mount_test.go
index 06e0216ede..6177d35615 100644
--- a/pkg/osbuild/mount_test.go
+++ b/pkg/osbuild/mount_test.go
@@ -1,10 +1,13 @@
 package osbuild_test
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
+	"github.com/osbuild/images/internal/common"
 	"github.com/osbuild/images/pkg/osbuild"
 )
 
@@ -55,3 +58,38 @@ func TestNewMounts(t *testing.T) {
 		assert.Equal(expected, actual)
 	}
 }
+
+func TestMountJsonAll(t *testing.T) {
+	mnt := &osbuild.Mount{
+		Name:   "xfs",
+		Type:   "org.osbuild.xfs",
+		Source: "/dev/sda4",
+		Target: "/mnt/xfs",
+		//TODO: test "Options:" too
+		Partition: common.ToPtr(1),
+	}
+	json, err := json.MarshalIndent(mnt, "", "  ")
+	require.Nil(t, err)
+	assert.Equal(t, string(json), `
+{
+  "name": "xfs",
+  "type": "org.osbuild.xfs",
+  "source": "/dev/sda4",
+  "target": "/mnt/xfs",
+  "partition": 1
+}`[1:])
+}
+
+func TestMountJsonOmitEmptyHonored(t *testing.T) {
+	mnt := &osbuild.Mount{
+		Name: "xfs",
+		Type: "org.osbuild.xfs",
+	}
+	json, err := json.MarshalIndent(mnt, "", "  ")
+	require.Nil(t, err)
+	assert.Equal(t, string(json), `
+{
+  "name": "xfs",
+  "type": "org.osbuild.xfs"
+}`[1:])
+}