diff --git a/expression/builtin_arithmetic.go b/expression/builtin_arithmetic.go
index e834cad55bff..b21b9dc6a591 100644
--- a/expression/builtin_arithmetic.go
+++ b/expression/builtin_arithmetic.go
@@ -117,11 +117,13 @@ func setFlenDecimal4RealOrDecimal(ctx sessionctx.Context, retTp *types.FieldType
 			retTp.SetFlen(types.UnspecifiedLength)
 			return
 		}
-		digitsInt := mathutil.Max(a.GetFlen()-a.GetDecimal(), b.GetFlen()-b.GetDecimal())
 		if isMultiply {
-			digitsInt = a.GetFlen() - a.GetDecimal() + b.GetFlen() - b.GetDecimal()
+			digitsInt := a.GetFlen() - a.GetDecimal() + b.GetFlen() - b.GetDecimal()
+			retTp.SetFlenUnderLimit(digitsInt + retTp.GetDecimal())
+		} else {
+			digitsInt := mathutil.Max(a.GetFlen()-a.GetDecimal(), b.GetFlen()-b.GetDecimal())
+			retTp.SetFlenUnderLimit(digitsInt + retTp.GetDecimal() + 1)
 		}
-		retTp.SetFlenUnderLimit(digitsInt + retTp.GetDecimal() + 1)
 		if isReal {
 			retTp.SetFlen(mathutil.Min(retTp.GetFlen(), mysql.MaxRealWidth))
 			return
diff --git a/expression/builtin_arithmetic_test.go b/expression/builtin_arithmetic_test.go
index 564da2678ac5..0d79464ddb65 100644
--- a/expression/builtin_arithmetic_test.go
+++ b/expression/builtin_arithmetic_test.go
@@ -71,7 +71,7 @@ func TestSetFlenDecimal4RealOrDecimal(t *testing.T) {
 
 	setFlenDecimal4RealOrDecimal(mock.NewContext(), ret, &Constant{RetType: a}, &Constant{RetType: b}, true, true)
 	require.Equal(t, 1, ret.GetDecimal())
-	require.Equal(t, 6, ret.GetFlen())
+	require.Equal(t, 5, ret.GetFlen())
 
 	b.SetFlen(65)
 	setFlenDecimal4RealOrDecimal(mock.NewContext(), ret, &Constant{RetType: a}, &Constant{RetType: b}, true, true)
diff --git a/expression/typeinfer_test.go b/expression/typeinfer_test.go
index 7e0a69e260b4..b2554c4f3d54 100644
--- a/expression/typeinfer_test.go
+++ b/expression/typeinfer_test.go
@@ -742,9 +742,9 @@ func (s *InferTypeSuite) createTestCase4ArithmeticFuncs() []typeInferTestCase {
 		{"c_int_d * c_char", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, types.UnspecifiedLength, types.UnspecifiedLength},
 		{"c_int_d * c_time_d", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxIntWidth, 0},
 		{"c_int_d * c_double_d", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, types.UnspecifiedLength, types.UnspecifiedLength},
-		{"c_int_d * c_decimal", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 17, 3},
-		{"c_datetime * c_decimal", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 29, 5},
-		{"c_bigint_d * c_decimal", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 27, 3},
+		{"c_int_d * c_decimal", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 16, 3},
+		{"c_datetime * c_decimal", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 28, 5},
+		{"c_bigint_d * c_decimal", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 26, 3},
 		{"c_double_d * c_decimal", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, types.UnspecifiedLength, types.UnspecifiedLength},
 		{"c_double_d * c_char", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, types.UnspecifiedLength, types.UnspecifiedLength},
 		{"c_double_d * c_enum", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, types.UnspecifiedLength, types.UnspecifiedLength},