diff --git a/internal/domain/scope.go b/internal/domain/scope.go
index e1d40f0..f8fb7ea 100644
--- a/internal/domain/scope.go
+++ b/internal/domain/scope.go
@@ -3,6 +3,7 @@ package domain
 import (
 	"errors"
 	"fmt"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -133,6 +134,18 @@ func (s *Scopes) UnmarshalJSON(v []byte) error {
 	return nil
 }
 
+func (s Scopes) MarshalJSON() ([]byte, error) {
+	scopes := make([]string, len(s))
+
+	for i := range s {
+		scopes[i] = s[i].String()
+	}
+
+	sort.Strings(scopes)
+
+	return []byte(strconv.Quote(strings.Join(scopes, " "))), nil
+}
+
 // String returns scope slug as string.
 func (s Scope) String() string {
 	return s.slug
diff --git a/internal/domain/scope_test.go b/internal/domain/scope_test.go
index acfeaf1..f765821 100644
--- a/internal/domain/scope_test.go
+++ b/internal/domain/scope_test.go
@@ -1,16 +1,16 @@
 package domain_test
 
 import (
-	"encoding/json"
 	"testing"
 
+	"github.com/goccy/go-json"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"source.toby3d.me/website/indieauth/internal/domain"
 )
 
-func TestScopesUnmarshalJSON(t *testing.T) {
+func TestScopes_UnmarshalJSON(t *testing.T) {
 	t.Parallel()
 
 	result := &struct {