diff --git a/expression/builtin_cast_vec.go b/expression/builtin_cast_vec.go
index 32dd7f32f863c..94ddc97007549 100644
--- a/expression/builtin_cast_vec.go
+++ b/expression/builtin_cast_vec.go
@@ -192,11 +192,10 @@ func (b *builtinCastTimeAsDecimalSig) vecEvalDecimal(input *chunk.Chunk, result
 		if result.IsNull(i) {
 			continue
 		}
-		decimalValue, err := types.ProduceDecWithSpecifiedTp(times[i].ToNumber(), b.tp, sc)
-		if err != nil {
+		times[i].FillNumber(&decs[i])
+		if _, err := types.ProduceDecWithSpecifiedTp(&decs[i], b.tp, sc); err != nil {
 			return err
 		}
-		decs[i] = *decimalValue
 	}
 	return nil
 }
diff --git a/types/time.go b/types/time.go
index 0a34b4f870584..746e0507fb460 100644
--- a/types/time.go
+++ b/types/time.go
@@ -292,8 +292,17 @@ const dateFormat = "%Y%m%d"
 // 2012-12-12T10:10:10 -> 20121212101010
 // 2012-12-12T10:10:10.123456 -> 20121212101010.123456
 func (t Time) ToNumber() *MyDecimal {
+	dec := new(MyDecimal)
+	t.FillNumber(dec)
+	return dec
+}
+
+// FillNumber is the same as ToNumber,
+// but reuses input decimal instead of allocating one.
+func (t Time) FillNumber(dec *MyDecimal) {
 	if t.IsZero() {
-		return &MyDecimal{}
+		dec.FromInt(0)
+		return
 	}
 
 	// Fix issue #1046
@@ -314,12 +323,9 @@ func (t Time) ToNumber() *MyDecimal {
 		s1 := fmt.Sprintf("%s.%06d", s, t.Time.Microsecond())
 		s = s1[:len(s)+int(t.Fsp)+1]
 	}
-
 	// We skip checking error here because time formatted string can be parsed certainly.
-	dec := new(MyDecimal)
 	err = dec.FromString([]byte(s))
 	terror.Log(errors.Trace(err))
-	return dec
 }
 
 // Convert converts t with type tp.