diff --git a/src/Symfony/Component/HttpFoundation/CHANGELOG.md b/src/Symfony/Component/HttpFoundation/CHANGELOG.md
index fdbd39cead31..29bc7507e58b 100644
--- a/src/Symfony/Component/HttpFoundation/CHANGELOG.md
+++ b/src/Symfony/Component/HttpFoundation/CHANGELOG.md
@@ -6,6 +6,7 @@ CHANGELOG
 
  * Add stale while revalidate and stale if error cache header
  * Allow dynamic session "ttl" when using a remote storage
+ * Send `Content-Length` when calling `Response::send()` and the content is a non-empty string
 
 6.0
 ---
diff --git a/src/Symfony/Component/HttpFoundation/Response.php b/src/Symfony/Component/HttpFoundation/Response.php
index e452e1a017f3..da5cec540522 100644
--- a/src/Symfony/Component/HttpFoundation/Response.php
+++ b/src/Symfony/Component/HttpFoundation/Response.php
@@ -371,6 +371,10 @@ public function sendContent(): static
      */
     public function send(): static
     {
+        if (\is_string($this->content) && '' !== $this->content && !$this->headers->has('Transfer-Encoding')) {
+            $this->headers->set('Content-Length', \strlen($this->content));
+        }
+
         $this->sendHeaders();
         $this->sendContent();
 
diff --git a/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php b/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
index af4b29e042f7..9d4a32a54269 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
@@ -50,13 +50,27 @@ public function testSendHeaders()
     public function testSend()
     {
         $response = new Response();
-        $responseSend = $response->send();
-        $this->assertObjectHasAttribute('headers', $responseSend);
-        $this->assertObjectHasAttribute('content', $responseSend);
-        $this->assertObjectHasAttribute('version', $responseSend);
-        $this->assertObjectHasAttribute('statusCode', $responseSend);
-        $this->assertObjectHasAttribute('statusText', $responseSend);
-        $this->assertObjectHasAttribute('charset', $responseSend);
+        $responseSent = $response->send();
+        $this->assertObjectHasAttribute('headers', $responseSent);
+        $this->assertObjectHasAttribute('content', $responseSent);
+        $this->assertObjectHasAttribute('version', $responseSent);
+        $this->assertObjectHasAttribute('statusCode', $responseSent);
+        $this->assertObjectHasAttribute('statusText', $responseSent);
+        $this->assertObjectHasAttribute('charset', $responseSent);
+        $this->assertFalse($responseSent->headers->has('Content-Length'));
+
+        ob_start();
+
+        $response = new Response('foo');
+        $responseSent = $response->send();
+        $this->assertSame('3', $responseSent->headers->get('Content-Length'));
+
+        $response = new Response('bar');
+        $response->headers->set('Transfer-Encoding', 'chunked');
+        $responseSent = $response->send();
+        $this->assertFalse($responseSent->headers->has('Content-Length'));
+
+        $this->assertSame('foobar', ob_get_clean());
     }
 
     public function testGetCharset()