diff --git a/src/Turbo/src/Helper/TurboStream.php b/src/Turbo/src/Helper/TurboStream.php
index 4ac16a27e2..8d183835b2 100644
--- a/src/Turbo/src/Helper/TurboStream.php
+++ b/src/Turbo/src/Helper/TurboStream.php
@@ -37,7 +37,7 @@ public static function prepend(string $target, string $html): string
      */
     public static function replace(string $target, string $html, bool $morph = false): string
     {
-        return self::custom('replace', $target, $html, $morph ? ['method="morph"'] : []);
+        return self::custom('replace', $target, $html, $morph ? ['method' => 'morph'] : []);
     }
 
     /**
@@ -45,7 +45,7 @@ public static function replace(string $target, string $html, bool $morph = false
      */
     public static function update(string $target, string $html, bool $morph = false): string
     {
-        return self::custom('update', $target, $html, $morph ? ['method="morph"'] : []);
+        return self::custom('update', $target, $html, $morph ? ['method' => 'morph'] : []);
     }
 
     /**
@@ -87,17 +87,33 @@ public static function refresh(?string $requestId = null): string
     }
 
     /**
-     * @param array<string> $attr
+     * Custom action and attributes.
+     *
+     * @param array<string, string|int|null> $attr
      */
     public static function custom(string $action, string $target, string $html, array $attr = []): string
     {
-        // Join array elements with a space and prepend a leading space
-        $atrrString = empty($attr) ? '' : ' '.implode(' ', $attr);
+        if (\array_key_exists('action', $attr) || \array_key_exists('targets', $attr)) {
+            throw new \InvalidArgumentException('The "action" and "targets" attributes are reserved and cannot be used.');
+        }
+
+        $attr['action'] = $action;
+        $attr['targets'] = $target;
+        $attr = array_merge(['action' => $action, 'targets' => $target], $attr);
+
+        $attrString = '';
+        foreach ($attr as $key => $value) {
+            if (null === $value) {
+                $attrString .= \sprintf(' %s', $key);
+            } else {
+                $attrString .= \sprintf(' %s="%s"', $key, \is_string($value) ? htmlspecialchars($value) : $value);
+            }
+        }
 
         return \sprintf(<<<EOHTML
-            <turbo-stream action="%s" targets="%s"%s>
+            <turbo-stream%s>
                 <template>%s</template>
             </turbo-stream>
-            EOHTML, $action, htmlspecialchars($target), $atrrString, $html);
+            EOHTML, $attrString, $html);
     }
 }
diff --git a/src/Turbo/tests/Helper/TurboStreamTest.php b/src/Turbo/tests/Helper/TurboStreamTest.php
index 8683f9fb2d..66cd25b396 100644
--- a/src/Turbo/tests/Helper/TurboStreamTest.php
+++ b/src/Turbo/tests/Helper/TurboStreamTest.php
@@ -11,6 +11,8 @@
 
 namespace Symfony\UX\Turbo\Tests\Helper;
 
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\TestWith;
 use PHPUnit\Framework\TestCase;
 use Symfony\UX\Turbo\Helper\TurboStream;
 
@@ -84,7 +86,24 @@ public function testCustom(): void
                 <template><div>content</div></template>
             </turbo-stream>
             EOHTML,
-            TurboStream::custom('customAction', 'some["selector"]', '<div>content</div>', ['someAttr="someValue"', 'boolAttr'])
+            TurboStream::custom('customAction', 'some["selector"]', '<div>content</div>', ['someAttr' => 'someValue', 'boolAttr' => null])
         );
     }
+
+    /**
+     * @dataProvider customThrowsExceptionDataProvider
+     *
+     * @param array<string, string|int|null> $attr
+     */
+    public function testCustomThrowsException(string $action, string $target, string $html, array $attr): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        TurboStream::custom($action, $target, $html, $attr);
+    }
+
+    public static function customThrowsExceptionDataProvider(): \Generator
+    {
+        yield ['customAction', 'some["selector"]', '<div>content</div>', ['action' => 'someAction']];
+        yield ['customAction', 'some["selector"]', '<div>content</div>', ['targets' => 'someTargets']];
+    }
 }