diff --git a/src/utils/index.ts b/src/utils/index.ts
index 44952a2..da92fa4 100644
--- a/src/utils/index.ts
+++ b/src/utils/index.ts
@@ -82,7 +82,7 @@ function lexer(input: string): Token[] {
             let value = '';
             const start = current;
 
-            while (char !== '\n') {
+            while (char !== '\n' && current < input.length) {
                 value += char;
                 char = input[++current];
             }
diff --git a/test/utils/index.test.ts b/test/utils/index.test.ts
index 3b69ff6..c50d9b4 100644
--- a/test/utils/index.test.ts
+++ b/test/utils/index.test.ts
@@ -1,4 +1,5 @@
 import { lexer, splitSql, cleanSql } from '../../src';
+import { TokenType } from '../../src/utils/token';
 
 describe('utils', () => {
     test('split single sql', () => {
@@ -28,6 +29,15 @@ describe('utils', () => {
         const result = lexer(sql);
         expect(result.length).toEqual(4);
     });
+    test('lexer for comments', () => {
+        const sql = `select * from a;--comments`;
+        const expected = `--comments`;
+        const result = lexer(sql);
+        const comments = result.find((token) =>
+            token.type === TokenType.Comment,
+        );
+        expect(comments.value).toEqual(expected);
+    });
     test('cleanSql', () => {
         const sql = `-- a ;
         select * from a;