diff --git a/common/json/internal/contextjson/unmarshal.go b/common/json/internal/contextjson/unmarshal.go
new file mode 100644
index 0000000..2940539
--- /dev/null
+++ b/common/json/internal/contextjson/unmarshal.go
@@ -0,0 +1,12 @@
+package json
+
+func UnmarshalDisallowUnknownFields(data []byte, v any) error {
+	var d decodeState
+	d.disallowUnknownFields = true
+	err := checkValid(data, &d.scan)
+	if err != nil {
+		return err
+	}
+	d.init(data)
+	return d.unmarshal(v)
+}
diff --git a/common/json/unmarshal.go b/common/json/unmarshal.go
index fa6452d..7505ebc 100644
--- a/common/json/unmarshal.go
+++ b/common/json/unmarshal.go
@@ -2,6 +2,7 @@ package json
 
 import (
 	"bytes"
+	"errors"
 	"strings"
 
 	"github.com/sagernet/sing/common"
@@ -15,7 +16,8 @@ func UnmarshalExtended[T any](content []byte) (T, error) {
 	if err == nil {
 		return value, err
 	}
-	if syntaxError, isSyntaxError := err.(*SyntaxError); isSyntaxError {
+	var syntaxError *SyntaxError
+	if errors.As(err, &syntaxError) {
 		prefix := string(content[:syntaxError.Offset])
 		row := strings.Count(prefix, "\n") + 1
 		column := len(prefix) - strings.LastIndex(prefix, "\n") - 1
diff --git a/common/json/unmarshal_context.go b/common/json/unmarshal_context.go
new file mode 100644
index 0000000..01f7962
--- /dev/null
+++ b/common/json/unmarshal_context.go
@@ -0,0 +1,9 @@
+//go:build go1.20 && !without_contextjson
+
+package json
+
+import (
+	json "github.com/sagernet/sing/common/json/internal/contextjson"
+)
+
+var UnmarshalDisallowUnknownFields = json.UnmarshalDisallowUnknownFields
diff --git a/common/json/unmarshal_std.go b/common/json/unmarshal_std.go
new file mode 100644
index 0000000..a4d36f4
--- /dev/null
+++ b/common/json/unmarshal_std.go
@@ -0,0 +1,13 @@
+//go:build !go1.20 || without_contextjson
+
+package json
+
+import (
+	"bytes"
+)
+
+func UnmarshalDisallowUnknownFields(content []byte, value any) error {
+	decoder := NewDecoder(bytes.NewReader(content))
+	decoder.DisallowUnknownFields()
+	return decoder.Decode(value)
+}