diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
index 835a0d6df3..926f3e41b1 100644
--- a/src/wp-includes/pluggable.php
+++ b/src/wp-includes/pluggable.php
@@ -454,7 +454,7 @@ if ( ! function_exists( 'wp_mail' ) ) :
 		if ( ! empty( $headers ) ) {
 			foreach ( (array) $headers as $name => $content ) {
 				// Only add custom headers not added automatically by PHPMailer.
-				if ( ! in_array( $name, array( 'MIME-Version', 'X-Mailer') ) ) {
+				if ( ! in_array( $name, array( 'MIME-Version', 'X-Mailer' ) ) ) {
 					$phpmailer->addCustomHeader( sprintf( '%1$s: %2$s', $name, $content ) );
 				}
 			}