diff --git a/.werks/15933 b/.werks/15933
new file mode 100644
index 0000000000000..5b3303ee70bc8
--- /dev/null
+++ b/.werks/15933
@@ -0,0 +1,16 @@
+Title: Fix failed LDAP sync because of invalid user ID
+Class: fix
+Compatible: compat
+Component: wato
+Date: 1691489253
+Edition: cre
+Knowledge: doc
+Level: 1
+Version: 2.3.0b1
+
+Since 2.2, user IDs are validated when synchronizing LDAP connections. This
+could result in a failed sync if one or more user IDs were invalid.
+
+From now on such users are skipped on synchronizing and logged to
+~/var/log/web.log.
+
diff --git a/cmk/gui/userdb/ldap_connector.py b/cmk/gui/userdb/ldap_connector.py
index 6f64601514b2d..07d2705676716 100644
--- a/cmk/gui/userdb/ldap_connector.py
+++ b/cmk/gui/userdb/ldap_connector.py
@@ -915,7 +915,13 @@ def get_users(self, add_filter: str = "") -> Users:
                     _('The configured User-ID attribute "%s" does not exist for the user "%s"')
                     % (user_id_attr, dn)
                 )
-            user_id = self._sanitize_user_id(ldap_user[user_id_attr][0])
+
+            try:
+                user_id = self._sanitize_user_id(ldap_user[user_id_attr][0])
+            except ValueError as e:
+                self._logger.warning(f"  SKIP SYNC {e}")
+                continue
+
             if user_id:
                 ldap_user["dn"] = dn  # also add the DN
                 result[user_id] = cast(UserSpec, ldap_user)
diff --git a/tests/unit/cmk/gui/userdb/ldap_golden.py b/tests/unit/cmk/gui/userdb/ldap_golden.py
index d7d848a7fd144..7f4d631ed354b 100644
--- a/tests/unit/cmk/gui/userdb/ldap_golden.py
+++ b/tests/unit/cmk/gui/userdb/ldap_golden.py
@@ -140,7 +140,10 @@ def _mock_simple_bind_s(mocker: MockerFixture, connector: LDAPUserConnector) ->
 
 
 def test_get_users(mocker: MockerFixture, mock_ldap: MagicMock) -> None:
-    ldap_result = [("user1", {"uid": ["USER1_ID"]})]
+    ldap_result = [
+        ("user1", {"uid": ["USER1_ID"]}),
+        ("user2", {"uid": ["USER2_ID#"]}),  # user with invalid user ID
+    ]
     # note that the key is lower-cased due to 'lower_user_ids'
     expected_result = {"user1_id": {"dn": "user1", "uid": ["USER1_ID"]}}
     add_filter = "my(*)filter"