diff --git a/src/Symfony/Component/Mime/Email.php b/src/Symfony/Component/Mime/Email.php
index 952c7b5c151ca..bfc7c37f1b043 100644
--- a/src/Symfony/Component/Mime/Email.php
+++ b/src/Symfony/Component/Mime/Email.php
@@ -460,8 +460,17 @@ private function prepareParts(): ?array
         if (null !== $this->html) {
             $htmlPart = new TextPart($html, $this->htmlCharset, 'html');
             $html = $htmlPart->getBody();
-            preg_match_all('(<img\s+[^>]*src\s*=\s*(?:([\'"])cid:([^"]+)\\1|cid:([^>\s]+)))i', $html, $names);
-            $names = array_filter(array_unique(array_merge($names[2], $names[3])));
+
+            $regexes = [
+                '<img\s+[^>]*src\s*=\s*(?:([\'"])cid:([^"]+)\\1|cid:([^>\s]+))',
+                '<\w+\s+[^>]*background\s*=\s*(?:([\'"])cid:([^"]+)\\1|cid:([^>\s]+))',
+            ];
+            $tmpMatches = [];
+            foreach ($regexes as $regex) {
+                preg_match_all('/'.$regex.'/i', $html, $tmpMatches);
+                $names = array_merge($names, $tmpMatches[2], $tmpMatches[3]);
+            }
+            $names = array_filter(array_unique($names));
         }
 
         $attachmentParts = $inlineParts = [];
diff --git a/src/Symfony/Component/Mime/Tests/EmailTest.php b/src/Symfony/Component/Mime/Tests/EmailTest.php
index e5b48fe6cabdc..ea06c7f6c12f5 100644
--- a/src/Symfony/Component/Mime/Tests/EmailTest.php
+++ b/src/Symfony/Component/Mime/Tests/EmailTest.php
@@ -351,6 +351,14 @@ public function testGenerateBody()
         // 2 parts only, not 3 (text + embedded image once)
         $this->assertCount(2, $parts = $body->getParts());
         $this->assertStringMatchesFormat('html content <img src=3D"cid:%s@symfony">', $parts[0]->bodyToString());
+
+        $e = (new Email())->from('me@example.com')->to('you@example.com');
+        $e->html('<div background="cid:test.gif"></div>');
+        $e->embed($image, 'test.gif');
+        $body = $e->getBody();
+        $this->assertInstanceOf(RelatedPart::class, $body);
+        $this->assertCount(2, $parts = $body->getParts());
+        $this->assertStringMatchesFormat('<div background=3D"cid:%s@symfony"></div>', $parts[0]->bodyToString());
     }
 
     public function testAttachments()