diff --git a/src/Symfony/Component/Mime/RawMessage.php b/src/Symfony/Component/Mime/RawMessage.php
index 66788d8ad526d..d2a311daebecf 100644
--- a/src/Symfony/Component/Mime/RawMessage.php
+++ b/src/Symfony/Component/Mime/RawMessage.php
@@ -33,8 +33,11 @@ public function toString(): string
         if (\is_string($this->message)) {
             return $this->message;
         }
+        if ($this->message instanceof \Traversable) {
+            $this->message = iterator_to_array($this->message, false);
+        }
 
-        return $this->message = implode('', iterator_to_array($this->message, false));
+        return $this->message = implode('', $this->message);
     }
 
     public function toIterable(): iterable
diff --git a/src/Symfony/Component/Mime/Tests/RawMessageTest.php b/src/Symfony/Component/Mime/Tests/RawMessageTest.php
index 26e7605baba2d..41503451bb1da 100644
--- a/src/Symfony/Component/Mime/Tests/RawMessageTest.php
+++ b/src/Symfony/Component/Mime/Tests/RawMessageTest.php
@@ -16,16 +16,12 @@
 
 class RawMessageTest extends TestCase
 {
-    public function testToString()
+    /**
+     * @dataProvider provideMessages
+     */
+    public function testToString($messageParameter)
     {
-        $message = new RawMessage('string');
-        $this->assertEquals('string', $message->toString());
-        $this->assertEquals('string', implode('', iterator_to_array($message->toIterable())));
-        // calling methods more than once work
-        $this->assertEquals('string', $message->toString());
-        $this->assertEquals('string', implode('', iterator_to_array($message->toIterable())));
-
-        $message = new RawMessage(new \ArrayObject(['some', ' ', 'string']));
+        $message = new RawMessage($messageParameter);
         $this->assertEquals('some string', $message->toString());
         $this->assertEquals('some string', implode('', iterator_to_array($message->toIterable())));
         // calling methods more than once work
@@ -33,6 +29,15 @@ public function testToString()
         $this->assertEquals('some string', implode('', iterator_to_array($message->toIterable())));
     }
 
+    public function provideMessages(): array
+    {
+        return [
+            'string' => ['some string'],
+            'traversable' => [new \ArrayObject(['some', ' ', 'string'])],
+            'array' => [['some', ' ', 'string']],
+        ];
+    }
+
     public function testSerialization()
     {
         $message = new RawMessage('string');