diff --git a/src/Header/OptimalEncodedHeaderValue.php b/src/Header/OptimalEncodedHeaderValue.php
index 5abd8b28..0e89425d 100644
--- a/src/Header/OptimalEncodedHeaderValue.php
+++ b/src/Header/OptimalEncodedHeaderValue.php
@@ -52,8 +52,8 @@ public function __construct(string $value, bool $phrase = false)
                         '=?%s?Q?%s?=',
                         'UTF-8',
                         \preg_replace(
-                            ['/\?/', '/_/', '/(?<!^) /m'],
-                            ['=3F', '=5F', '_'],
+                            ['/\?/', '/_/', '/&/', '/(?<!^) /m'],
+                            ['=3F', '=5F', '=26', '_'],
                             (string) $encoded
                         )
                     )
diff --git a/test/Unit/Header/SubjectTest.php b/test/Unit/Header/SubjectTest.php
index e85cacfa..e01eaf90 100644
--- a/test/Unit/Header/SubjectTest.php
+++ b/test/Unit/Header/SubjectTest.php
@@ -75,6 +75,21 @@ public function it_encodes_underscores_with_quoted_printable_encoding(): void
         );
     }
 
+    /**
+     * @test
+     */
+    public function it_encodes_ampersand_with_quoted_printable_encoding(): void
+    {
+        $subject = new Subject(
+            'Aaaaaaaaaaa 20 aaaaa Aaaaaaaaaaa ‘Aaaaaaaaaaaaaa Aaaaaaaa & Aaaaaaaaa’'
+        );
+
+        $this->assertEquals(
+            "=?UTF-8?Q?Aaaaaaaaaaa_20_aaaaa_Aaaaaaaaaaa_=E2=80=98Aaaaaaaaaaaaaa_Aaaaaaaa_=26?=\r\n =?UTF-8?Q?_Aaaaaaaaa=E2=80=99?=",
+            (string)$subject->getValue()
+        );
+    }
+
     /**
      * @return array
      */