diff --git a/pythonlib/camoufox/ip.py b/pythonlib/camoufox/ip.py
index b9045dd..6a64a31 100644
--- a/pythonlib/camoufox/ip.py
+++ b/pythonlib/camoufox/ip.py
@@ -2,6 +2,7 @@ import re
 from dataclasses import dataclass
 from functools import lru_cache
 from typing import Dict, Optional, Tuple
+from urllib.parse import quote
 
 import requests
 
@@ -38,10 +39,12 @@ class Proxy:
         if not schema:
             schema = 'http'
         result = f"{schema}://"
+        # Percent-encode the credentials: a raw `#`, `/`, `?` or `@` breaks the
+        # URL, and a raw `%XX` is decoded into a different password.
         if self.username:
-            result += f"{self.username}"
+            result += quote(self.username, safe='')
             if self.password:
-                result += f":{self.password}"
+                result += f":{quote(self.password, safe='')}"
             result += "@"
 
         result += url
diff --git a/pythonlib/tests/test_proxy_geo.py b/pythonlib/tests/test_proxy_geo.py
index 0b8dbfb..2e46a5c 100644
--- a/pythonlib/tests/test_proxy_geo.py
+++ b/pythonlib/tests/test_proxy_geo.py
@@ -11,6 +11,7 @@ timezone while its traffic went through the proxy:
 
 import asyncio
 from unittest import mock
+from urllib.parse import unquote, urlsplit
 
 import pytest
 
@@ -75,6 +76,18 @@ def test_lookup_goes_through_the_proxy_with_its_credentials(api, server, expecte
     assert "203.0.113.7" in context.add_init_script.call_args.args[0]
 
 
+@pytest.mark.parametrize("api", ["sync", "async"])
+def test_credentials_with_url_delimiters_survive_the_proxy_url(api):
+    # A raw `#`, `/` or `?` stops the URL parsing, and a raw `%41` would be
+    # decoded into a different password (#823).
+    username, password = "us@r name", "p#ss/w?rd:%41"
+    with mock.patch.object(ip.requests, "get", return_value=_Response(EXIT)) as get:
+        _new_context(api, {"server": "proxy.example.com:8080", "username": username, "password": password})
+    url = urlsplit(get.call_args.kwargs["proxies"]["https"])
+    assert (url.hostname, url.port) == ("proxy.example.com", 8080)
+    assert (unquote(url.username), unquote(url.password)) == (username, password)
+
+
 @pytest.mark.parametrize("api", ["sync", "async"])
 @pytest.mark.parametrize(
     "failure",
diff --git a/typescript/src/ip.ts b/typescript/src/ip.ts
index cffee9a..b9beaae 100644
--- a/typescript/src/ip.ts
+++ b/typescript/src/ip.ts
@@ -37,10 +37,12 @@ export class ProxyHelper {
 	static asString(proxy: ProxyConfig): string {
 		const { schema, url, port } = ProxyHelper.parseServer(proxy.server);
 		let result = `${schema}://`;
+		// Percent-encode the credentials: a raw `#`, `/`, `?` or `@` breaks the
+		// URL, and a raw `%XX` is decoded into a different password.
 		if (proxy.username) {
-			result += proxy.username;
+			result += encodeURIComponent(proxy.username);
 			if (proxy.password) {
-				result += `:${proxy.password}`;
+				result += `:${encodeURIComponent(proxy.password)}`;
 			}
 			result += "@";
 		}
diff --git a/typescript/tests/proxy-geo.test.ts b/typescript/tests/proxy-geo.test.ts
index d58804f..520a5fd 100644
--- a/typescript/tests/proxy-geo.test.ts
+++ b/typescript/tests/proxy-geo.test.ts
@@ -74,6 +74,22 @@ describe("NewContext proxy lookup", () => {
 		expect(calls.script).toContain("203.0.113.7");
 	});
 
+	it("credentials with URL delimiters survive the proxy URL", async () => {
+		// A raw `#`, `/` or `?` stops the URL parsing, and a raw `%41` would be
+		// decoded into a different password (#823).
+		const username = "us@r name";
+		const password = "p#ss/w?rd:%41";
+		const { browser } = fakeBrowser();
+		await NewContext(browser, {
+			os: "linux",
+			proxy: { server: "proxy.example.com:8080", username, password },
+		});
+		const url = new URL(impit.proxyUrls[0] as string);
+		expect([url.hostname, url.port]).toEqual(["proxy.example.com", "8080"]);
+		expect(decodeURIComponent(url.username)).toBe(username);
+		expect(decodeURIComponent(url.password)).toBe(password);
+	});
+
 	it.each([
 		[
 			"an unreachable proxy",