diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9887cd190e..56b7ed674e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,15 @@
 # v1.19
 
+## Release v1.19.1 - TBD
+
+### Bug fix
+
+* http_server helper: Fix IPv6 bind address support in URI construction
+  * Fixed `URI::InvalidURIError` when binding to IPv6 addresses (e.g., `::`, `::1`)
+  * IPv6 addresses are now properly bracketed in URIs per RFC 3986 (e.g., `http://[::]:24231`)
+  * Handles pre-bracketed addresses correctly to avoid double-bracketing
+  * Affects all plugins using http_server helper with IPv6 bind addresses
+
 ## Release v1.19.0 - 2025/07/30
 
 ### Enhancement
diff --git a/lib/fluent/plugin_helper/http_server/server.rb b/lib/fluent/plugin_helper/http_server/server.rb
index 9c099292d8..b59450c242 100644
--- a/lib/fluent/plugin_helper/http_server/server.rb
+++ b/lib/fluent/plugin_helper/http_server/server.rb
@@ -37,7 +37,16 @@ def initialize(addr:, port:, logger:, default_app: nil, tls_context: nil)
 
           # TODO: support http2
           scheme = tls_context ? 'https' : 'http'
-          @uri = URI("#{scheme}://#{@addr}:#{@port}").to_s
+          # Handle IPv6 addresses properly in URI construction per RFC 3986
+          # Check if address is already bracketed to avoid double-bracketing
+          addr_display = if @addr.include?(":") && !@addr.start_with?('[')
+                           "[#{@addr}]"  # Bare IPv6 address - add brackets
+                         elsif @addr.start_with?('[') && @addr.end_with?(']')
+                           @addr         # Already bracketed - use as-is
+                         else
+                           @addr         # IPv4 or hostname - use directly
+                         end
+          @uri = URI("#{scheme}://#{addr_display}:#{@port}").to_s
           @router = Router.new(default_app)
           @server_task = nil
           Console.logger = Fluent::Log::ConsoleAdapter.wrap(@logger)
diff --git a/test/plugin_helper/test_http_server_helper.rb b/test/plugin_helper/test_http_server_helper.rb
index bc9853c013..f71400ded3 100644
--- a/test/plugin_helper/test_http_server_helper.rb
+++ b/test/plugin_helper/test_http_server_helper.rb
@@ -21,6 +21,22 @@ def teardown
     @port = nil
   end
 
+  def ipv6_enabled?
+    begin
+      # Try to actually bind to an IPv6 address to verify it works
+      sock = Socket.new(Socket::AF_INET6, Socket::SOCK_STREAM, 0)
+      sock.bind(Socket.sockaddr_in(0, '::1'))
+      sock.close
+      
+      # Also test that we can resolve IPv6 addresses
+      # This is needed because some systems can bind but can't connect
+      Socket.getaddrinfo('::1', nil, Socket::AF_INET6)
+      true
+    rescue Errno::EADDRNOTAVAIL, Errno::EAFNOSUPPORT, SocketError
+      false
+    end
+  end
+
   class Dummy < Fluent::Plugin::TestBase
     helpers :http_server
   end
@@ -364,6 +380,57 @@ def start_https_request(addr, port, verify: true, cert_path: nil, selfsigned: tr
       end
     end
 
+    test 'bind to IPv6 address' do
+      omit('IPv6 not supported') unless ipv6_enabled?
+      on_driver do |driver|
+        driver.http_server_create_http_server(:http_server_helper_test, addr: '::1', port: @port, logger: NULL_LOGGER) do |s|
+          s.get('/example/hello') { [200, { 'Content-Type' => 'text/plain' }, 'hello from ipv6'] }
+        end
+        resp = get("http://[::1]:#{@port}/example/hello")
+        assert_equal('200', resp.code)
+        assert_equal('hello from ipv6', resp.body)
+      end
+    end
+
+    test 'bind to IPv6 wildcard address' do
+      omit('IPv6 not supported') unless ipv6_enabled?
+      on_driver do |driver|
+        driver.http_server_create_http_server(:http_server_helper_test, addr: '::', port: @port, logger: NULL_LOGGER) do |s|
+          s.get('/example/hello') { [200, { 'Content-Type' => 'text/plain' }, 'hello from ipv6 wildcard'] }
+        end
+        # Can access via IPv4-mapped IPv6 or IPv6 loopback
+        resp = get("http://[::1]:#{@port}/example/hello")
+        assert_equal('200', resp.code)
+        assert_equal('hello from ipv6 wildcard', resp.body)
+      end
+    end
+
+    test 'handle already bracketed IPv6 address' do
+      omit('IPv6 not supported') unless ipv6_enabled?
+      on_driver do |driver|
+        # Test that pre-bracketed addresses don't get double-bracketed
+        driver.http_server_create_http_server(:http_server_helper_test, addr: '[::1]', port: @port, logger: NULL_LOGGER) do |s|
+          s.get('/example/hello') { [200, { 'Content-Type' => 'text/plain' }, 'hello from bracketed ipv6'] }
+        end
+        resp = get("http://[::1]:#{@port}/example/hello")
+        assert_equal('200', resp.code)
+        assert_equal('hello from bracketed ipv6', resp.body)
+      end
+    end
+
+    test 'handle already bracketed IPv6 wildcard address' do
+      omit('IPv6 not supported') unless ipv6_enabled?
+      on_driver do |driver|
+        driver.http_server_create_http_server(:http_server_helper_test, addr: '[::]', port: @port, logger: NULL_LOGGER) do |s|
+          s.get('/example/hello') { [200, { 'Content-Type' => 'text/plain' }, 'hello from bracketed ipv6 wildcard'] }
+        end
+        # Access via IPv6 loopback
+        resp = get("http://[::1]:#{@port}/example/hello")
+        assert_equal('200', resp.code)
+        assert_equal('hello from bracketed ipv6 wildcard', resp.body)
+      end
+    end
+
     test 'must be called #start and #stop' do
       on_driver do |driver|
         server = flexmock('Server') do |watcher|