diff --git a/dbms/src/Functions/FunctionsTiDBConversion.h b/dbms/src/Functions/FunctionsTiDBConversion.h
index 51a79102313..bf31705b4a1 100644
--- a/dbms/src/Functions/FunctionsTiDBConversion.h
+++ b/dbms/src/Functions/FunctionsTiDBConversion.h
@@ -842,11 +842,11 @@ struct TiDBConvertToDecimal
     template <typename U>
     static U toTiDBDecimal(MyDateTime & date_time, PrecType prec, ScaleType scale, int fsp, const Context & context)
     {
-        UInt64 value_without_fsp = date_time.year * 10000000000ULL + date_time.month * 100000000ULL + date_time.day * 100000
-            + date_time.hour * 1000 + date_time.minute * 100 + date_time.second;
+        UInt64 value_without_fsp = date_time.year * 10000000000ULL + date_time.month * 100000000ULL + date_time.day * 1000000ULL
+            + date_time.hour * 10000ULL + date_time.minute * 100 + date_time.second;
         if (fsp > 0)
         {
-            Int128 value = value_without_fsp * 1000000 + date_time.micro_second;
+            Int128 value = static_cast<Int128>(value_without_fsp) * 1000000 + date_time.micro_second;
             Decimal128 decimal(value);
             return toTiDBDecimal<Decimal128, U>(decimal, 6, prec, scale, context);
         }
diff --git a/tests/fullstack-test/expr/cast_as_decimal.test b/tests/fullstack-test/expr/cast_as_decimal.test
new file mode 100644
index 00000000000..f0985e3cad3
--- /dev/null
+++ b/tests/fullstack-test/expr/cast_as_decimal.test
@@ -0,0 +1,23 @@
+mysql> drop table if exists test.t1;
+mysql> create table test.t1(c1 datetime(5));
+mysql> insert into test.t1 values('2022-10-10 10:10:10.12345');
+mysql> alter table test.t1 set tiflash replica 1;
+func> wait_table test t1
+mysql> set @@tidb_isolation_read_engines='tiflash'; set @@tidb_enforce_mpp = 1; select cast(test.t1.c1 as decimal(16, 3)) from test.t1;
++------------------------------------+
+| cast(test.t1.c1 as decimal(16, 3)) |
++------------------------------------+
+|                  9999999999999.999 |
++------------------------------------+
+mysql> set @@tidb_isolation_read_engines='tiflash'; set @@tidb_enforce_mpp = 1; select cast(test.t1.c1 as decimal(17, 3)) from test.t1;
++------------------------------------+
+| cast(test.t1.c1 as decimal(17, 3)) |
++------------------------------------+
+|                 20221010101010.123 |
++------------------------------------+
+mysql> set @@tidb_isolation_read_engines='tiflash'; set @@tidb_enforce_mpp = 1; select cast(test.t1.c1 as decimal(18, 3)) from test.t1;
++------------------------------------+
+| cast(test.t1.c1 as decimal(18, 3)) |
++------------------------------------+
+|                 20221010101010.123 |
++------------------------------------+