diff --git a/diagnose.go b/diagnose.go
index f164e099..dcb03002 100644
--- a/diagnose.go
+++ b/diagnose.go
@@ -111,8 +111,6 @@ func (opts DiagOptions) diagMode() (*diagMode, error) {
 		MaxNestedLevels:  opts.MaxNestedLevels,
 		MaxArrayElements: opts.MaxArrayElements,
 		MaxMapPairs:      opts.MaxMapPairs,
-		// loosest decode options for diagnostic purpose.
-		UTF8: UTF8DecodeInvalid,
 	}.decMode()
 	if err != nil {
 		return nil, err
diff --git a/diagnose_test.go b/diagnose_test.go
index dc4b9ca3..742e8efa 100644
--- a/diagnose_test.go
+++ b/diagnose_test.go
@@ -583,14 +583,6 @@ func TestDiagnoseTextString(t *testing.T) {
 				ByteStringText: true,
 			},
 		},
-		// {
-		// 	"invalid UTF-8 text in text string",
-		// 	hexDecode("6d68656c6c6fffeee4bda0e5a5bd"),
-		// 	`"hello\u00ff\u00ee\u4f60\u597d"`,
-		// 	&DiagOptions{
-		// 		ByteStringText: true,
-		// 	},
-		// },
 		{
 			"valid grapheme cluster text in byte string",
 			hexDecode("583448656c6c6f2c2027e29da4efb88fe2808df09f94a5270ae4bda0e5a5bdefbc8c22f09fa791e2808df09fa49de2808df09fa79122"),
@@ -615,14 +607,6 @@ func TestDiagnoseTextString(t *testing.T) {
 				ByteStringText: true,
 			},
 		},
-		// {
-		// 	"invalid grapheme cluster text in text string",
-		// 	hexDecode("783448656c6c6feeff27e29da4efb88fe2808df09f94a5270de4bda0e5a5bdefbc8c22f09fa791e2808df09fa49de2808df09fa79122"),
-		// 	`"Hello\u00ee\u00ff'\u2764\ufe0f\u200d\ud83d\udd25'\r\u4f60\u597d\uff0c\"\ud83e\uddd1\u200d\ud83e\udd1d\u200d\ud83e\uddd1\""`,
-		// 	&DiagOptions{
-		// 		ByteStringText: true,
-		// 	},
-		// },
 		{
 			"indefinite length text string with no chunks",
 			hexDecode("7fff"),