diff --git a/src/engine.ts b/src/engine.ts
index 4934f165..edbb03d5 100644
--- a/src/engine.ts
+++ b/src/engine.ts
@@ -935,7 +935,9 @@ function dynamicReplacement(
 	const _pipe = _config_rr.pipedData,
 		_text = _data_rr,
 		_find = _config_rr.pattern,
-		code_rr = _config_rr.replacementOri,
+		// The code of the user is in a block of its own, so it can declare the same names with let and const.
+		// The value of the block is the value of its last statement, like before. The line break ends a comment at the end.
+		code_rr = '{' + _config_rr.replacementOri + '\n}',
 		_cwd = process.cwd(),
 		_now = _time,
 		_ = ' ',
diff --git a/test/fix/815.test.js b/test/fix/815.test.js
new file mode 100644
index 00000000..3c882816
--- /dev/null
+++ b/test/fix/815.test.js
@@ -0,0 +1,23 @@
+// https://github.com/mathiasrw/rexreplace/issues/815
+// The numbers and the named groups were made with var in front of the code, so code that declared the same name with let or const did not run.
+import {describe, test, expect} from 'bun:test';
+import {rr} from '../helper.js';
+
+describe('#815 --js code can declare its own variables', () => {
+	test.each([
+		['a cousin with const', 'o', 'const $n00 = "C"; $n00', 'fCC'],
+		['a number with var, as before', 'o', 'var $t = "V"; $t', 'fVV'],
+		['a function', 'o', 'function $t() { return "F"; } $t()', 'fFF'],
+		['a number with let', 'o', 'let $t = "T"; $t', 'fTT'],
+		['a group with const', '(o)', 'const $1 = "X"; $1', 'fXX'],
+		['a named group with let', '(?<o>o)', 'let _o = "N"; _o', 'fNN'],
+	])('with the name of %s', async (name, pattern, code, out) => {
+		expect((await rr(pattern, code, {pipedData: 'foo', replacementJs: true})).out).toBe(out);
+	});
+
+	test('the value is still the value of the last statement, also with a comment at the end', async () => {
+		expect(
+			(await rr('o', 'const a = 1; a + 1 // two', {pipedData: 'foo', replacementJs: true})).out
+		).toBe('f22');
+	});
+});