diff --git a/problems/0018.四数之和.md b/problems/0018.四数之和.md
index 2146a114..99613070 100644
--- a/problems/0018.四数之和.md
+++ b/problems/0018.四数之和.md
@@ -153,7 +153,7 @@ class Solution {
                 int left = j + 1;
                 int right = nums.length - 1;
                 while (right > left) {
-                    int sum = nums[i] + nums[j] + nums[left] + nums[right];
+                    long sum = (long) nums[i] + nums[j] + nums[left] + nums[right];
                     if (sum > target) {
                         right--;
                     } else if (sum < target) {