diff --git a/expression/builtin_arithmetic_vec.go b/expression/builtin_arithmetic_vec.go
index 7bc9ea867a0c1..7981eabe6e835 100644
--- a/expression/builtin_arithmetic_vec.go
+++ b/expression/builtin_arithmetic_vec.go
@@ -881,7 +881,7 @@ func (b *builtinArithmeticPlusIntSig) plusUS(result *chunk.Column, lhi64s, rhi64
 		if rh < 0 && uint64(-rh) > uint64(lh) {
 			return types.ErrOverflow.GenWithStackByArgs("BIGINT UNSIGNED", fmt.Sprintf("(%s + %s)", b.args[0].String(), b.args[1].String()))
 		}
-		if rh > 0 && uint64(lh) > math.MaxUint64-uint64(lh) {
+		if rh > 0 && uint64(lh) > math.MaxUint64-uint64(rh) {
 			return types.ErrOverflow.GenWithStackByArgs("BIGINT UNSIGNED", fmt.Sprintf("(%s + %s)", b.args[0].String(), b.args[1].String()))
 		}
 
diff --git a/expression/integration_test.go b/expression/integration_test.go
index 4a35f580e30c9..f9557b1c574cd 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -9216,6 +9216,12 @@ func (s *testIntegrationSuite) TestRefineArgNullValues(c *C) {
 	))
 }
 
+func (s *testIntegrationSuite) TestIssue26977(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	result := tk.MustQuery("select a + 1 as f from (select cast(0xfffffffffffffff0 as unsigned) as a union select cast(1 as unsigned)) t having f != 2;")
+	result.Check(testkit.Rows("18446744073709551601"))
+}
+
 func (s *testIntegrationSuite) TestIssue26958(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test;")