diff --git a/src/Server/Handler/Request/ResourceSubscribeHandler.php b/src/Server/Handler/Request/ResourceSubscribeHandler.php
index b5421f87..1e8147b0 100644
--- a/src/Server/Handler/Request/ResourceSubscribeHandler.php
+++ b/src/Server/Handler/Request/ResourceSubscribeHandler.php
@@ -18,6 +18,7 @@
 use Mcp\Schema\JsonRpc\Response;
 use Mcp\Schema\Request\ResourceSubscribeRequest;
 use Mcp\Schema\Result\EmptyResult;
+use Mcp\Server\RequestContext;
 use Mcp\Server\Resource\SubscriptionManagerInterface;
 use Mcp\Server\Session\SessionInterface;
 use Psr\Log\LoggerInterface;
@@ -57,7 +58,9 @@ public function handle(Request $request, SessionInterface $session): Response|Er
         } catch (ResourceNotFoundException $e) {
             $this->logger->error('Resource not found', ['uri' => $uri, 'exception' => $e]);
 
-            return Error::forResourceNotFound($e->getMessage(), $request->getId());
+            return (new RequestContext($session, $request))->getProtocolVersion()->usesInvalidParamsForResourceNotFound()
+                ? Error::forInvalidParams($e->getMessage(), $request->getId(), ['uri' => $uri])
+                : Error::forResourceNotFound($e->getMessage(), $request->getId());
         }
 
         $this->logger->debug('Subscribing to resource', ['uri' => $uri]);
diff --git a/src/Server/Handler/Request/ResourceUnsubscribeHandler.php b/src/Server/Handler/Request/ResourceUnsubscribeHandler.php
index 50ab8bc1..522c5128 100644
--- a/src/Server/Handler/Request/ResourceUnsubscribeHandler.php
+++ b/src/Server/Handler/Request/ResourceUnsubscribeHandler.php
@@ -18,6 +18,7 @@
 use Mcp\Schema\JsonRpc\Response;
 use Mcp\Schema\Request\ResourceUnsubscribeRequest;
 use Mcp\Schema\Result\EmptyResult;
+use Mcp\Server\RequestContext;
 use Mcp\Server\Resource\SubscriptionManagerInterface;
 use Mcp\Server\Session\SessionInterface;
 use Psr\Log\LoggerInterface;
@@ -57,7 +58,9 @@ public function handle(Request $request, SessionInterface $session): Response|Er
         } catch (ResourceNotFoundException $e) {
             $this->logger->error('Resource not found', ['uri' => $uri, 'exception' => $e]);
 
-            return Error::forResourceNotFound($e->getMessage(), $request->getId());
+            return (new RequestContext($session, $request))->getProtocolVersion()->usesInvalidParamsForResourceNotFound()
+                ? Error::forInvalidParams($e->getMessage(), $request->getId(), ['uri' => $uri])
+                : Error::forResourceNotFound($e->getMessage(), $request->getId());
         }
 
         $this->logger->debug('Unsubscribing from resource', ['uri' => $uri]);
diff --git a/tests/Unit/Server/Handler/Request/ResourceSubscribeHandlerTest.php b/tests/Unit/Server/Handler/Request/ResourceSubscribeHandlerTest.php
new file mode 100644
index 00000000..d16519ec
--- /dev/null
+++ b/tests/Unit/Server/Handler/Request/ResourceSubscribeHandlerTest.php
@@ -0,0 +1,127 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Unit\Server\Handler\Request;
+
+use Mcp\Capability\RegistryInterface;
+use Mcp\Exception\ResourceNotFoundException;
+use Mcp\Schema\JsonRpc\Error;
+use Mcp\Schema\JsonRpc\Response;
+use Mcp\Schema\Request\ResourceSubscribeRequest;
+use Mcp\Schema\Result\EmptyResult;
+use Mcp\Server\Handler\Request\ResourceSubscribeHandler;
+use Mcp\Server\Resource\SubscriptionManagerInterface;
+use Mcp\Server\Session\SessionInterface;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+class ResourceSubscribeHandlerTest extends TestCase
+{
+    private ResourceSubscribeHandler $handler;
+    private RegistryInterface&MockObject $registry;
+    private SubscriptionManagerInterface&MockObject $subscriptionManager;
+    private SessionInterface&MockObject $session;
+    private LoggerInterface&MockObject $logger;
+
+    protected function setUp(): void
+    {
+        $this->registry = $this->createMock(RegistryInterface::class);
+        $this->subscriptionManager = $this->createMock(SubscriptionManagerInterface::class);
+        $this->session = $this->createMock(SessionInterface::class);
+        $this->logger = $this->createMock(LoggerInterface::class);
+
+        $this->handler = new ResourceSubscribeHandler($this->registry, $this->subscriptionManager, $this->logger);
+    }
+
+    public function testSupportsResourceSubscribeRequest(): void
+    {
+        $request = $this->createRequest('file://test.txt');
+
+        $this->assertTrue($this->handler->supports($request));
+    }
+
+    public function testHandleSuccessfulSubscribe(): void
+    {
+        $uri = 'file://test.txt';
+        $request = $this->createRequest($uri);
+
+        $this->registry
+            ->expects($this->once())
+            ->method('getResource')
+            ->with($uri)
+            ->willReturn($this->createMock(\Mcp\Capability\Registry\ResourceReference::class));
+
+        $this->subscriptionManager
+            ->expects($this->once())
+            ->method('subscribe')
+            ->with($this->session, $uri);
+
+        $response = $this->handler->handle($request, $this->session);
+
+        $this->assertInstanceOf(Response::class, $response);
+        $this->assertEquals($request->getId(), $response->id);
+        $this->assertInstanceOf(EmptyResult::class, $response->result);
+    }
+
+    /**
+     * @dataProvider provideResourceNotFoundRevisions
+     */
+    public function testHandleResourceNotFoundIsProtocolVersionAware(?string $negotiated, int $expectedCode): void
+    {
+        $uri = 'file://nonexistent/file.txt';
+        $request = $this->createRequest($uri);
+        $exception = new ResourceNotFoundException($uri);
+
+        $this->registry
+            ->expects($this->once())
+            ->method('getResource')
+            ->with($uri)
+            ->willThrowException($exception);
+
+        $this->session
+            ->method('get')
+            ->with('protocol_version')
+            ->willReturn($negotiated);
+
+        $this->subscriptionManager
+            ->expects($this->never())
+            ->method('subscribe');
+
+        $response = $this->handler->handle($request, $this->session);
+
+        $this->assertInstanceOf(Error::class, $response);
+        $this->assertEquals($request->getId(), $response->id);
+        $this->assertEquals($expectedCode, $response->code);
+    }
+
+    /**
+     * @return iterable<string, array{?string, int}>
+     */
+    public static function provideResourceNotFoundRevisions(): iterable
+    {
+        yield 'no negotiated revision' => [null, Error::RESOURCE_NOT_FOUND];
+        yield '2025-11-25' => ['2025-11-25', Error::RESOURCE_NOT_FOUND];
+        yield '2026-07-28' => ['2026-07-28', Error::INVALID_PARAMS];
+    }
+
+    private function createRequest(string $uri): ResourceSubscribeRequest
+    {
+        return ResourceSubscribeRequest::fromArray([
+            'jsonrpc' => '2.0',
+            'method' => ResourceSubscribeRequest::getMethod(),
+            'id' => 'test-request-'.uniqid(),
+            'params' => [
+                'uri' => $uri,
+            ],
+        ]);
+    }
+}
diff --git a/tests/Unit/Server/Handler/Request/ResourceUnsubscribeHandlerTest.php b/tests/Unit/Server/Handler/Request/ResourceUnsubscribeHandlerTest.php
new file mode 100644
index 00000000..daa82f52
--- /dev/null
+++ b/tests/Unit/Server/Handler/Request/ResourceUnsubscribeHandlerTest.php
@@ -0,0 +1,127 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Tests\Unit\Server\Handler\Request;
+
+use Mcp\Capability\RegistryInterface;
+use Mcp\Exception\ResourceNotFoundException;
+use Mcp\Schema\JsonRpc\Error;
+use Mcp\Schema\JsonRpc\Response;
+use Mcp\Schema\Request\ResourceUnsubscribeRequest;
+use Mcp\Schema\Result\EmptyResult;
+use Mcp\Server\Handler\Request\ResourceUnsubscribeHandler;
+use Mcp\Server\Resource\SubscriptionManagerInterface;
+use Mcp\Server\Session\SessionInterface;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+class ResourceUnsubscribeHandlerTest extends TestCase
+{
+    private ResourceUnsubscribeHandler $handler;
+    private RegistryInterface&MockObject $registry;
+    private SubscriptionManagerInterface&MockObject $subscriptionManager;
+    private SessionInterface&MockObject $session;
+    private LoggerInterface&MockObject $logger;
+
+    protected function setUp(): void
+    {
+        $this->registry = $this->createMock(RegistryInterface::class);
+        $this->subscriptionManager = $this->createMock(SubscriptionManagerInterface::class);
+        $this->session = $this->createMock(SessionInterface::class);
+        $this->logger = $this->createMock(LoggerInterface::class);
+
+        $this->handler = new ResourceUnsubscribeHandler($this->registry, $this->subscriptionManager, $this->logger);
+    }
+
+    public function testSupportsResourceUnsubscribeRequest(): void
+    {
+        $request = $this->createRequest('file://test.txt');
+
+        $this->assertTrue($this->handler->supports($request));
+    }
+
+    public function testHandleSuccessfulUnsubscribe(): void
+    {
+        $uri = 'file://test.txt';
+        $request = $this->createRequest($uri);
+
+        $this->registry
+            ->expects($this->once())
+            ->method('getResource')
+            ->with($uri)
+            ->willReturn($this->createMock(\Mcp\Capability\Registry\ResourceReference::class));
+
+        $this->subscriptionManager
+            ->expects($this->once())
+            ->method('unsubscribe')
+            ->with($this->session, $uri);
+
+        $response = $this->handler->handle($request, $this->session);
+
+        $this->assertInstanceOf(Response::class, $response);
+        $this->assertEquals($request->getId(), $response->id);
+        $this->assertInstanceOf(EmptyResult::class, $response->result);
+    }
+
+    /**
+     * @dataProvider provideResourceNotFoundRevisions
+     */
+    public function testHandleResourceNotFoundIsProtocolVersionAware(?string $negotiated, int $expectedCode): void
+    {
+        $uri = 'file://nonexistent/file.txt';
+        $request = $this->createRequest($uri);
+        $exception = new ResourceNotFoundException($uri);
+
+        $this->registry
+            ->expects($this->once())
+            ->method('getResource')
+            ->with($uri)
+            ->willThrowException($exception);
+
+        $this->session
+            ->method('get')
+            ->with('protocol_version')
+            ->willReturn($negotiated);
+
+        $this->subscriptionManager
+            ->expects($this->never())
+            ->method('unsubscribe');
+
+        $response = $this->handler->handle($request, $this->session);
+
+        $this->assertInstanceOf(Error::class, $response);
+        $this->assertEquals($request->getId(), $response->id);
+        $this->assertEquals($expectedCode, $response->code);
+    }
+
+    /**
+     * @return iterable<string, array{?string, int}>
+     */
+    public static function provideResourceNotFoundRevisions(): iterable
+    {
+        yield 'no negotiated revision' => [null, Error::RESOURCE_NOT_FOUND];
+        yield '2025-11-25' => ['2025-11-25', Error::RESOURCE_NOT_FOUND];
+        yield '2026-07-28' => ['2026-07-28', Error::INVALID_PARAMS];
+    }
+
+    private function createRequest(string $uri): ResourceUnsubscribeRequest
+    {
+        return ResourceUnsubscribeRequest::fromArray([
+            'jsonrpc' => '2.0',
+            'method' => ResourceUnsubscribeRequest::getMethod(),
+            'id' => 'test-request-'.uniqid(),
+            'params' => [
+                'uri' => $uri,
+            ],
+        ]);
+    }
+}