diff --git a/changedetectionio/tests/unit/test_validate_url.py b/changedetectionio/tests/unit/test_validate_url.py
new file mode 100644
index 00000000..616413b8
--- /dev/null
+++ b/changedetectionio/tests/unit/test_validate_url.py
@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+
+# run from dir above changedetectionio/ dir
+# python3 -m unittest changedetectionio.tests.unit.test_validate_url
+
+import unittest
+
+from changedetectionio.validate_url import is_safe_valid_url, normalize_url_encoding
+
+
+class TestValidateUrl(unittest.TestCase):
+
+    def test_fragment_with_pipe_characters_is_valid(self):
+        """https://github.com/dgtlmoon/changedetection.io/issues/4209
+        Browsers accept '|' in the fragment/anchor but RFC 3986 does not,
+        so it must be percent-encoded before validation instead of rejected."""
+        url = 'https://www.fnac.com/Pack-Tablette-Tactile-Samsung-Galaxy-Tab-S10-Lite-10-9-Wi-Fi-128-Go-Anthracite-Book-Cover/a21903823/w-4#int=S:PFreco|PF|48966|21903823|BL4|L1'
+        self.assertTrue(is_safe_valid_url(url), f"URL '{url}' with '|' in the fragment should be valid")
+
+    def test_fragment_pipe_is_percent_encoded(self):
+        normalized = normalize_url_encoding('https://example.com/page#a|b')
+        self.assertEqual(normalized, 'https://example.com/page#a%7Cb')
+
+    def test_already_encoded_fragment_is_not_double_encoded(self):
+        normalized = normalize_url_encoding('https://example.com/page#a%7Cb')
+        self.assertEqual(normalized, 'https://example.com/page#a%7Cb')
+
+    def test_fragment_normalization_is_idempotent(self):
+        url = 'https://example.com/page#int=S:PFreco|PF|48966'
+        once = normalize_url_encoding(url)
+        twice = normalize_url_encoding(once)
+        self.assertEqual(once, twice)
+
+    def test_rfc3986_fragment_characters_are_untouched(self):
+        # pchar / "/" / "?" are all legal in a fragment and must survive as-is
+        urls = [
+            'https://example.com/docs#section-2.1',
+            'https://example.com/app#/route/sub?tab=1',
+            "https://example.com/page#key=val&other=a:b@c!$&'()*+,;=",
+        ]
+        for url in urls:
+            with self.subTest(url=url):
+                self.assertEqual(normalize_url_encoding(url), url)
+                self.assertTrue(is_safe_valid_url(url))
+
+    def test_unsafe_urls_are_still_rejected(self):
+        # The fragment fix must not loosen any of the existing security checks
+        unsafe = [
+            'javascript:alert(1)',
+            'source:javascript:alert(1)',
+            'https://example.com/page#<script>',
+            'http://INTERNAL:8888\\@PUBLIC/',
+            '',
+            None,
+        ]
+        for url in unsafe:
+            with self.subTest(url=url):
+                self.assertFalse(is_safe_valid_url(url), f"URL '{url}' should be rejected")
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/changedetectionio/validate_url.py b/changedetectionio/validate_url.py
index 85dfd25e..d8e7b51f 100644
--- a/changedetectionio/validate_url.py
+++ b/changedetectionio/validate_url.py
@@ -2,7 +2,7 @@ import ipaddress
 import socket
 from functools import lru_cache
 from loguru import logger
-from urllib.parse import urlparse, urlunparse, parse_qsl, urlencode
+from urllib.parse import urlparse, urlunparse, parse_qsl, urlencode, quote, unquote
 
 
 def normalize_url_encoding(url):
@@ -41,6 +41,13 @@ def normalize_url_encoding(url):
         # Re-encode the query string properly using standard URL encoding
         encoded_query = urlencode(query_params, safe='')
 
+        # Fragments need the same treatment - browsers accept characters there that
+        # RFC 3986 does not (e.g. '|' in "...w-4#int=S:PFreco|PF|48966", see issue #4209)
+        # and validators.url() would reject them. unquote() first so an already-encoded
+        # fragment isn't double-encoded, then re-quote keeping every character that
+        # RFC 3986 allows in a fragment (pchar / "/" / "?") intact.
+        encoded_fragment = quote(unquote(parsed.fragment), safe="/?:@!$&'()*+,;=")
+
         # Reconstruct the URL with properly encoded query string
         normalized = urlunparse((
             parsed.scheme,
@@ -48,7 +55,7 @@ def normalize_url_encoding(url):
             parsed.path,
             parsed.params,
             encoded_query,  # Use the re-encoded query
-            parsed.fragment
+            encoded_fragment  # Use the re-encoded fragment
         ))
 
         return normalized