diff --git a/test/core/codec_test.dart b/test/core/codec_test.dart
index 7cd9f066..005f4d38 100644
--- a/test/core/codec_test.dart
+++ b/test/core/codec_test.dart
@@ -6,12 +6,13 @@
 
 import 'dart:convert';
 
+import 'package:dart_wot/scripting_api.dart';
 import 'package:dart_wot/src/core/codecs/text_codec.dart';
 import 'package:test/test.dart';
 
 void main() {
-  group('TextCodec', () {
-    test('should convert bytes to values and back', () {
+  group('TextCodec should', () {
+    test('convert bytes to values and back', () {
       final textCodec = TextCodec();
 
       const testValue = 'foo';
@@ -25,4 +26,24 @@ void main() {
       expect(convertedBytes, testInput);
     });
   });
+
+  test('reject unknown charsets', () {
+    final textCodec = TextCodec();
+
+    const charsetParameters = {'charset': 'foobar'};
+
+    expect(
+      () => textCodec.bytesToValue(utf8.encode('foo'), null, charsetParameters),
+      throwsFormatException,
+    );
+
+    expect(
+      () => textCodec.valueToBytes(
+        DataSchemaValue.fromNull(),
+        null,
+        charsetParameters,
+      ),
+      throwsFormatException,
+    );
+  });
 }