diff --git a/tests/phpunit/tests/mail.php b/tests/phpunit/tests/mail.php
index 25c49c1..b92f42e 100644
--- a/tests/phpunit/tests/mail.php
+++ b/tests/phpunit/tests/mail.php
@@ -23,6 +23,22 @@ class Tests_Mail extends WP_UnitTestCase {
 		$this->assertTrue( wp_mail( WP_TESTS_EMAIL, 'Looong line testing', $content ) );
 	}
 
+	/**
+	 * @ticket 33972
+	 */
+	function test_wp_mail_encoding_does_not_bleed() {
+		$content = str_repeat( 'A', 1000 );
+		wp_mail( WP_TESTS_EMAIL, 'Looong line testing', $content );
+	
+		$mailer = tests_retrieve_phpmailer_instance();
+		$this->assertEquals( 'quoted-printable', $mailer->Encoding );
+
+		wp_mail( WP_TESTS_EMAIL, 'A follow up short email', 'Short email' );
+
+		$mailer = tests_retrieve_phpmailer_instance();
+		$this->assertEquals( '8bit', $mailer->Encoding );
+	}
+
 	function test_wp_mail_custom_boundaries() {
 		$to = 'user@example.com';
 		$subject = 'Test email with custom boundaries';