diff --git a/src/Slim/Middleware/FrameAncestorsCspHeader.php b/src/Slim/Middleware/FrameAncestorsCspHeader.php
new file mode 100644
index 0000000..92ea93d
--- /dev/null
+++ b/src/Slim/Middleware/FrameAncestorsCspHeader.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace Serato\SwsApp\Slim\Middleware;
+
+use Psr\Http\Message\RequestInterface as Request;
+use Psr\Http\Message\ResponseInterface as Response;
+use Slim\Handlers\AbstractHandler;
+
+/**
+ * Class FrameAncestorsCspHeader
+ *
+ * Adds a CSP header with frame-ancestors rule, which gets merged with the other CSP rules by a browser.
+ * Applications where this middleware is used, can't be framed inside a frame or iframe tag.
+ *
+ * @package App\Middleware
+ */
+class FrameAncestorsCspHeader extends AbstractHandler
+{
+    /**
+     * Invoke the middleware
+     *
+     * @param Request           $request   The most recent Request object
+     * @param Response          $response  The most recent Response object
+     * @param Callable          $next      The next middleware to call
+     *
+     * @return Response
+     */
+    public function __invoke(Request $request, Response $response, callable $next): Response
+    {
+        $response = $next($request, $response);
+        $response = $response
+            ->withAddedHeader('Content-Security-Policy', "frame-ancestors 'none';");
+
+        return $response;
+    }
+}
diff --git a/tests/Slim/Middleware/FrameAncestorsCspHeaderTest.php b/tests/Slim/Middleware/FrameAncestorsCspHeaderTest.php
new file mode 100644
index 0000000..f796b09
--- /dev/null
+++ b/tests/Slim/Middleware/FrameAncestorsCspHeaderTest.php
@@ -0,0 +1,72 @@
+<?php
+
+namespace Serato\SwsApp\Test\Slim\Middleware;
+
+use Serato\SwsApp\Test\TestCase;
+use Serato\SwsApp\Slim\Middleware\EmptyWare;
+use Serato\Slimulator\EnvironmentBuilder;
+use Serato\Slimulator\Request;
+use Slim\Http\Response;
+use Serato\SwsApp\Slim\Middleware\FrameAncestorsCspHeader;
+
+/**
+ * Class FrameAncestorsCspHeaderTest
+ * @package Serato\SwsApp\Test\Slim\Middleware
+ */
+class FrameAncestorsCspHeaderTest extends TestCase
+{
+    private const CSP_VALUE = "frame-ancestors 'none'";
+
+    /**
+     * Create an Request object and Response object.
+     *
+     * Execute the middleware and get the returned Response object.
+     *
+     * Confirm that the Response object has:
+     *
+     * - A `Content-Security-Policy` header whose value is always "frame-ancestors 'none';".
+     */
+    public function testWithOriginRequestHeader()
+    {
+        $middleware = new FrameAncestorsCspHeader();
+
+        $response = $middleware(
+            Request::createFromEnvironmentBuilder(EnvironmentBuilder::create()),
+            new Response(),
+            new EmptyWare()
+        );
+
+        $this->assertNotFalse(
+            strpos($response->getHeaderLine('Content-Security-Policy'), self::CSP_VALUE)
+        );
+    }
+
+    /**
+     * Create a Request object.
+     * Create a Response object with a `Content-Security-Policy` header that contains an initial value.
+     *
+     * Execute the middleware and get the returned Response object.
+     *
+     * Confirm that the Response object has:
+     *
+     * - A `Content-Security-Policy` header whose value contains both the initial value and "frame-ancestors 'none'".
+     */
+    public function testWithOriginRequestHeaderAndExistingCspResponseHeader()
+    {
+        $initialValue = "default-src 'none';";
+
+        $middleware = new FrameAncestorsCspHeader();
+
+        $response = new Response();
+        $response = $middleware(
+            Request::createFromEnvironmentBuilder(EnvironmentBuilder::create()),
+            $response->withHeader('Content-Security-Policy', $initialValue),
+            new EmptyWare()
+        );
+
+        $this->assertNotFalse(strpos($response->getHeaderLine('Content-Security-Policy'), $initialValue));
+        $this->assertNotFalse(
+            strpos($response->getHeaderLine('Content-Security-Policy'), self::CSP_VALUE)
+        );
+    }
+}