diff --git a/expression/builtin_time_vec.go b/expression/builtin_time_vec.go
index 529d0e47b8668..f5558aa20c770 100644
--- a/expression/builtin_time_vec.go
+++ b/expression/builtin_time_vec.go
@@ -1877,12 +1877,11 @@ func (b *builtinHourSig) vecEvalInt(input *chunk.Chunk, result *chunk.Column) er
 	result.ResizeInt64(n, false)
 	result.MergeNulls(buf)
 	i64s := result.Int64s()
-	ds := buf.GoDurations()
 	for i := 0; i < n; i++ {
 		if result.IsNull(i) {
 			continue
 		}
-		i64s[i] = int64(ds[i].Hours())
+		i64s[i] = int64(buf.GetDuration(i, int(types.UnspecifiedFsp)).Hour())
 	}
 	return nil
 }
diff --git a/expression/integration_test.go b/expression/integration_test.go
index 0bfa1008381e9..b558fe2148b1c 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -9284,6 +9284,19 @@ func (s *testIntegrationSuite) TestConstPropNullFunctions(c *C) {
 	tk.MustQuery("select * from t2 where t2.i2=((select count(1) from t1 where t1.i1=t2.i2))").Check(testkit.Rows("1 <nil> 0.1"))
 }
 
+func (s *testIntegrationSuite) TestIssue28643(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a time(4));")
+	tk.MustExec("insert into t values(\"-838:59:59.000000\");")
+	tk.MustExec("insert into t values(\"838:59:59.000000\");")
+	tk.MustExec("set tidb_enable_vectorized_expression = on;")
+	tk.MustQuery("select hour(a) from t;").Check(testkit.Rows("838", "838"))
+	tk.MustExec("set tidb_enable_vectorized_expression = off;")
+	tk.MustQuery("select hour(a) from t;").Check(testkit.Rows("838", "838"))
+}
+
 func (s *testIntegrationSuite) TestIssue29244(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")