diff --git a/lib/core/convert/index.ts b/lib/core/convert/index.ts
index 3ed4dd1..cc4374a 100644
--- a/lib/core/convert/index.ts
+++ b/lib/core/convert/index.ts
@@ -28,7 +28,7 @@ const toneMap = {
   ü: ['ü', 'ǖ', 'ǘ', 'ǚ', 'ǜ'],
   v: ['ü', 'ǖ', 'ǘ', 'ǚ', 'ǜ'],
   ui: ['ui', 'uī', 'uí', 'uǐ', 'uì'],
-  iu: ['iu', 'īu', 'íu', 'ǐu', 'ìu'],
+  iu: ['iu', 'iū', 'iú', 'iǔ', 'iù'],
   i: ['i', 'ī', 'í', 'ǐ', 'ì'],
   u: ['u', 'ū', 'ú', 'ǔ', 'ù'],
   n: ['n', 'n', 'ń', 'ň', 'ǹ'],
diff --git a/test/convert.test.js b/test/convert.test.js
index ff4de50..76c56ba 100644
--- a/test/convert.test.js
+++ b/test/convert.test.js
@@ -57,4 +57,9 @@ describe('convert', () => {
     const result = convert('l2', { format: 'numToSymbol' });
     expect(result).to.be.equal('l2');
   });
+
+  it('[convert]numToSymbol iu', () => {
+    const result = convert('liu2', { format: 'numToSymbol' });
+    expect(result).to.be.equal('liú');
+  });
 });