diff --git a/random/random.go b/random/random.go
index 6e0c8cf..230feb6 100644
--- a/random/random.go
+++ b/random/random.go
@@ -17,7 +17,7 @@ import (
 )
 
 const (
-	MaximumCapacity = 1 << 31
+	MaximumCapacity = math.MaxInt>>1 + 1
 	Numeral         = "0123456789"
 	LowwerLetters   = "abcdefghijklmnopqrstuvwxyz"
 	UpperLetters    = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
@@ -157,7 +157,7 @@ func random(s string, length int) string {
 			cache, remain = rn.Int63(), letterIdMax
 		}
 		// 从可用字符的字符串中随机选择一个字符
-		if idx := int(cache & letterIdMask); idx < len(s) {
+		if idx := int(cache & letterIdMask); idx < strLength {
 			bytes[i] = s[idx]
 			i--
 		}