diff --git a/src/decrypt/__test__/QmcCache.test.ts b/src/decrypt/__test__/QmcCache.test.ts
new file mode 100644
index 0000000..2cbc45d
--- /dev/null
+++ b/src/decrypt/__test__/QmcCache.test.ts
@@ -0,0 +1,20 @@
+import { DecryptBuffer as DecryptQmcCacheBuffer } from '../qmccache';
+import fs from 'fs';
+
+const expectedBuffer = fs.readFileSync(__dirname + '/fixture/qmc_cache_expected.bin');
+
+const createInputBuffer = () => {
+  const buffer = Buffer.alloc(256);
+  for (let i = buffer.byteLength; i >= 0; i--) {
+    buffer[i] = i;
+  }
+  return buffer;
+};
+
+describe('decrypt/qmccache', () => {
+  it('should decrypt specified buffer correctly', () => {
+    const input = createInputBuffer();
+    DecryptQmcCacheBuffer(input);
+    expect(input).toEqual(expectedBuffer);
+  });
+});
diff --git a/src/decrypt/__test__/fixture/qmc_cache_expected.bin b/src/decrypt/__test__/fixture/qmc_cache_expected.bin
new file mode 100644
index 0000000..a1a0f6d
Binary files /dev/null and b/src/decrypt/__test__/fixture/qmc_cache_expected.bin differ
diff --git a/src/decrypt/qmccache.ts b/src/decrypt/qmccache.ts
index 59bf5c1..9d44b4c 100644
--- a/src/decrypt/qmccache.ts
+++ b/src/decrypt/qmccache.ts
@@ -35,11 +35,9 @@ export async function Decrypt(file: Blob, raw_filename: string, raw_ext: string)
     musicDecoded = new Uint8Array(buffer);
     let length = musicDecoded.length;
     for (let i = 0; i < length; i++) {
-      musicDecoded[i] ^= 0xf4;
-      if (musicDecoded[i] <= 0x3f) musicDecoded[i] = musicDecoded[i] * 4;
-      else if (musicDecoded[i] <= 0x7f) musicDecoded[i] = (musicDecoded[i] - 0x40) * 4 + 1;
-      else if (musicDecoded[i] <= 0xbf) musicDecoded[i] = (musicDecoded[i] - 0x80) * 4 + 2;
-      else musicDecoded[i] = (musicDecoded[i] - 0xc0) * 4 + 3;
+      let byte = musicDecoded[i] ^ 0xf4; // xor 0xf4
+      byte = ((byte & 0b0011_1111) << 2) | (byte >> 6); // rol 2
+      musicDecoded[i] = byte;
     }
   }
   let ext = SniffAudioExt(musicDecoded, '');