diff --git a/src/ssn/decryption/modifyPassword.ts b/src/ssn/decryption/modifyPassword.ts
index 0f7e041..a5417d6 100644
--- a/src/ssn/decryption/modifyPassword.ts
+++ b/src/ssn/decryption/modifyPassword.ts
@@ -5,7 +5,7 @@ export default function modifyPassword(passwordIn: Uint8Array) {
 
   for (let i = 0; i < passwordLength; i += 1) {
     if (passwordIn[i] === 0) { break; }
-    let curChar = passwordIn[i] + (1 << (i % 32));
+    let curChar = passwordIn[i] + ((1 << (i % 32)) & 0xFF);
     if (curChar > 0x7E) {
       if (curChar === 0xFF || curChar === 0x7F) {
         curChar = 0x3F;