diff --git a/executor/write_test.go b/executor/write_test.go
index b832e52a9935c..cf7a51985a450 100644
--- a/executor/write_test.go
+++ b/executor/write_test.go
@@ -3930,6 +3930,25 @@ func (s *testSerialSuite) TestIssue20840(c *C) {
 	tk.MustExec("drop table t1")
 }
 
+func (s *testSerialSuite) TestIssueInsertPrefixIndexForNonUTF8Collation(c *C) {
+	collate.SetNewCollationEnabledForTest(true)
+	defer collate.SetNewCollationEnabledForTest(false)
+
+	tk := testkit.NewTestKitWithInit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1, t2, t3")
+	tk.MustExec("create table t1 ( c_int int, c_str varchar(40) character set ascii collate ascii_bin, primary key(c_int, c_str(8)) clustered , unique key(c_str))")
+	tk.MustExec("create table t2 ( c_int int, c_str varchar(40) character set latin1 collate latin1_bin, primary key(c_int, c_str(8)) clustered , unique key(c_str))")
+	tk.MustExec("insert into t1 values (3, 'fervent brattain')")
+	tk.MustExec("insert into t2 values (3, 'fervent brattain')")
+	tk.MustExec("admin check table t1")
+	tk.MustExec("admin check table t2")
+
+	tk.MustExec("create table t3 (x varchar(40) CHARACTER SET ascii COLLATE ascii_bin, UNIQUE KEY uk(x(4)))")
+	tk.MustExec("insert into t3 select 'abc '")
+	tk.MustGetErrCode("insert into t3 select 'abc d'", 1062)
+}
+
 func (s *testSerialSuite) TestIssue22496(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")
diff --git a/tablecodec/tablecodec.go b/tablecodec/tablecodec.go
index 215f8d05c27fa..de766831bc245 100644
--- a/tablecodec/tablecodec.go
+++ b/tablecodec/tablecodec.go
@@ -1292,6 +1292,7 @@ func TruncateIndexValue(v *types.Datum, idxCol *model.IndexColumn, tblCol *model
 	if notStringType {
 		return
 	}
+	originalKind := v.Kind()
 	isUTF8Charset := tblCol.Charset == charset.CharsetUTF8 || tblCol.Charset == charset.CharsetUTF8MB4
 	if isUTF8Charset && utf8.RuneCount(v.GetBytes()) > idxCol.Length {
 		rs := bytes.Runes(v.GetBytes())
@@ -1303,7 +1304,7 @@ func TruncateIndexValue(v *types.Datum, idxCol *model.IndexColumn, tblCol *model
 		}
 	} else if !isUTF8Charset && len(v.GetBytes()) > idxCol.Length {
 		v.SetBytes(v.GetBytes()[:idxCol.Length])
-		if v.Kind() == types.KindString {
+		if originalKind == types.KindString {
 			v.SetString(v.GetString(), tblCol.Collate)
 		}
 	}