diff --git a/src/wp-includes/user.php b/src/wp-includes/user.php
index 82b5013a08..858d4a065d 100644
--- a/src/wp-includes/user.php
+++ b/src/wp-includes/user.php
@@ -149,7 +149,11 @@ function wp_authenticate_username_password( $user, $username, $password ) {
 	if ( ! $user ) {
 		return new WP_Error(
 			'invalid_username',
-			__( '<strong>Error</strong>: Unknown username. Check again or try your email address.' )
+			sprintf(
+				/* translators: %s: User name. */
+				__( '<strong>Error</strong>: The username <strong>%s</strong> is not registered on this site. If you are unsure of your username, try your email address instead.' ),
+				$username
+			)
 		);
 	}