diff --git a/CHANGELOG.md b/CHANGELOG.md
index 67fffbc7..824690ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Fixed
+- Allow underscore and tilde in URI hostnames as per RFC 3986 ([#853](https://github.com/jsonrainbow/json-schema/pull/853))
 
 ## [6.6.1] - 2025-11-07
 ### Changed
diff --git a/src/JsonSchema/Tool/Validator/UriValidator.php b/src/JsonSchema/Tool/Validator/UriValidator.php
index b761f91f..c5e2cf6e 100644
--- a/src/JsonSchema/Tool/Validator/UriValidator.php
+++ b/src/JsonSchema/Tool/Validator/UriValidator.php
@@ -12,7 +12,7 @@ public static function isValid(string $uri): bool
         $hierarchicalPattern = '/^
             ([a-z][a-z0-9+\-.]*):\/\/                # Scheme (http, https, ftp, etc.)
             (?:([^:@\/?#]+)(?::([^@\/?#]*))?@)?      # Optional userinfo (user:pass@)
-            ([a-z0-9.-]+|\[[a-f0-9:.]+\])            # Hostname or IPv6 in brackets
+            ([a-z0-9._~-]+|\[[a-f0-9:.]+\])          # Hostname or IPv6 in brackets
             (?::(\d{1,5}))?                          # Optional port
             (\/[a-zA-Z0-9._~!$&\'()*+,;=:@\/%-]*)*   # Path (valid characters only)
             (\?([^#]*))?                             # Optional query
diff --git a/tests/Tool/Validator/UriValidatorTest.php b/tests/Tool/Validator/UriValidatorTest.php
index 13e99b85..7eedaca8 100644
--- a/tests/Tool/Validator/UriValidatorTest.php
+++ b/tests/Tool/Validator/UriValidatorTest.php
@@ -32,6 +32,8 @@ public function validUriDataProvider(): \Generator
         yield 'Data URI' => ['uri' => 'data:text/plain;charset=utf-8,Hello%20World!'];
         yield 'ISBN URN URI' => ['uri' => 'urn:isbn:0451450523'];
         yield 'OASIS URN URI' => ['uri' => 'urn:oasis:names:specification:docbook:dtd:xml:4.1.2'];
+        yield 'Custom URI with underscore' => ['uri' => 'custom://reg_name/path/file.json'];
+        yield 'Custom URI with tilde' => ['uri' => 'custom://reg~name/path/file.json'];
     }
 
     public function invalidUriDataProvider(): \Generator