diff --git a/wp-includes/user.php b/wp-includes/user.php
index 867df81e16..e0cfae9188 100644
--- a/wp-includes/user.php
+++ b/wp-includes/user.php
@@ -2123,10 +2123,16 @@ function wp_insert_user( $userdata ) {
 		return new WP_Error( 'user_login_too_long', __( 'Username may not be longer than 60 characters.' ) );
 	}
 
+	// Username must be unique.
 	if ( ! $update && username_exists( $user_login ) ) {
 		return new WP_Error( 'existing_user_login', __( 'Sorry, that username already exists!' ) );
 	}
 
+	// Username must not match an existing user email.
+	if ( email_exists( $user_login ) ) {
+		return new WP_Error( 'existing_user_login_as_email', __( 'Sorry, that username is not available.' ) );
+	}
+
 	/**
 	 * Filters the list of disallowed usernames.
 	 *
@@ -3340,7 +3346,8 @@ function register_new_user( $user_login, $user_email ) {
 		$sanitized_user_login = '';
 	} elseif ( username_exists( $sanitized_user_login ) ) {
 		$errors->add( 'username_exists', __( '<strong>Error:</strong> This username is already registered. Please choose another one.' ) );
-
+	} elseif ( email_exists( $sanitized_user_login ) ) {
+		$errors->add( 'username_exists_as_email', __( '<strong>Error:</strong> This username is not available. Please choose another one.' ) );
 	} else {
 		/** This filter is documented in wp-includes/user.php */
 		$illegal_user_logins = (array) apply_filters( 'illegal_user_logins', array() );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index c172abf486..1ce6ce4707 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-beta2-55356';
+$wp_version = '6.2-beta2-55358';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.