diff --git a/expression/integration_test.go b/expression/integration_test.go
index 71ecef6c6b692..5c45fe3edcdd8 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -4057,3 +4057,15 @@ func (s *testIntegrationSuite) TestIssue10181(c *C) {
 	tk.MustExec(`insert into t values(9223372036854775807), (18446744073709551615)`)
 	tk.MustQuery(`select * from t where a > 9223372036854775807-0.5 order by a`).Check(testkit.Rows(`9223372036854775807`, `18446744073709551615`))
 }
+
+// for issue #9770
+func (s *testIntegrationSuite) TestDecimalConvertToTime(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	defer s.cleanEnv(c)
+
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a datetime(6), b timestamp)")
+	tk.MustExec("insert t values (20010101100000.123456, 20110707101112.123456)")
+	tk.MustQuery("select * from t").Check(testkit.Rows("2001-01-01 10:00:00.123456 2011-07-07 10:11:12"))
+}
diff --git a/types/convert_test.go b/types/convert_test.go
index 51816860f2795..dd50805cb6122 100644
--- a/types/convert_test.go
+++ b/types/convert_test.go
@@ -628,7 +628,9 @@ func (s *testTypeConvertSuite) TestConvert(c *C) {
 	signedAccept(c, mysql.TypeDatetime, "2012-08-23 12:34:03.123456", "2012-08-23 12:34:03")
 	signedAccept(c, mysql.TypeDatetime, ZeroDatetime, "0000-00-00 00:00:00")
 	signedAccept(c, mysql.TypeDatetime, int64(0), "0000-00-00 00:00:00")
+	signedAccept(c, mysql.TypeDatetime, NewDecFromFloatForTest(20010101100000.123456), "2001-01-01 10:00:00")
 	signedAccept(c, mysql.TypeTimestamp, "2012-08-23 12:34:03.123456", "2012-08-23 12:34:03")
+	signedAccept(c, mysql.TypeTimestamp, NewDecFromFloatForTest(20010101100000.123456), "2001-01-01 10:00:00")
 	signedAccept(c, mysql.TypeDuration, "10:11:12", "10:11:12")
 	signedAccept(c, mysql.TypeDuration, ZeroDatetime, "00:00:00")
 	signedAccept(c, mysql.TypeDuration, ZeroDuration, "00:00:00")
diff --git a/types/datum.go b/types/datum.go
index 7fa790c4ded85..bea8aff87d2e2 100644
--- a/types/datum.go
+++ b/types/datum.go
@@ -948,6 +948,8 @@ func (d *Datum) convertToMysqlTimestamp(sc *stmtctx.StatementContext, target *Fi
 		t, err = ParseTime(sc, d.GetString(), mysql.TypeTimestamp, fsp)
 	case KindInt64:
 		t, err = ParseTimeFromNum(sc, d.GetInt64(), mysql.TypeTimestamp, fsp)
+	case KindMysqlDecimal:
+		t, err = ParseTimeFromFloatString(sc, d.GetMysqlDecimal().String(), mysql.TypeTimestamp, fsp)
 	default:
 		return invalidConv(d, mysql.TypeTimestamp)
 	}
@@ -985,6 +987,8 @@ func (d *Datum) convertToMysqlTime(sc *stmtctx.StatementContext, target *FieldTy
 			return ret, errors.Trace(err)
 		}
 		t, err = t.RoundFrac(sc, fsp)
+	case KindMysqlDecimal:
+		t, err = ParseTimeFromFloatString(sc, d.GetMysqlDecimal().String(), tp, fsp)
 	case KindString, KindBytes:
 		t, err = ParseTime(sc, d.GetString(), tp, fsp)
 	case KindInt64: