diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
index 1dbac5e1d707c..fcbdb3424b742 100644
--- a/src/wp-includes/pluggable.php
+++ b/src/wp-includes/pluggable.php
@@ -356,8 +356,9 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 		$phpmailer->clearAttachments();
 		$phpmailer->clearCustomHeaders();
 		$phpmailer->clearReplyTos();
-		$phpmailer->Body    = '';
-		$phpmailer->AltBody = '';
+		$phpmailer->Body     = '';
+		$phpmailer->AltBody  = '';
+		$phpmailer->Encoding = PHPMailer\PHPMailer\PHPMailer::ENCODING_8BIT;
 
 		// Set "From" name and email.
 
diff --git a/tests/phpunit/tests/pluggable/wpMail.php b/tests/phpunit/tests/pluggable/wpMail.php
index 7b88d739add22..4884837b189fd 100644
--- a/tests/phpunit/tests/pluggable/wpMail.php
+++ b/tests/phpunit/tests/pluggable/wpMail.php
@@ -554,4 +554,22 @@ public function test_wp_mail_resets_properties() {
 		$phpmailer = $GLOBALS['phpmailer'];
 		$this->assertNotSame( 'user1', $phpmailer->AltBody );
 	}
+
+	/**
+	 * Test that the encoding of the email does not bleed between long and short emails.
+	 *
+	 * @ticket 33972
+	 */
+	public 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 );
+	}
 }