diff --git a/wp-admin/network/user-new.php b/wp-admin/network/user-new.php
index 52e4d9fa7e..4b330c0819 100644
--- a/wp-admin/network/user-new.php
+++ b/wp-admin/network/user-new.php
@@ -89,7 +89,7 @@ if ( isset( $add_user_errors ) && is_wp_error( $add_user_errors ) ) { ?>
 	<table class="form-table">
 		<tr class="form-field form-required">
 			<th scope="row"><label for="username"><?php _e( 'Username' ) ?></label></th>
-			<td><input type="text" class="regular-text" name="user[username]" id="username" autocapitalize="none" autocorrect="off" /></td>
+			<td><input type="text" class="regular-text" name="user[username]" id="username" autocapitalize="none" autocorrect="off" maxlength="60" /></td>
 		</tr>
 		<tr class="form-field form-required">
 			<th scope="row"><label for="email"><?php _e( 'Email' ) ?></label></th>
diff --git a/wp-admin/user-new.php b/wp-admin/user-new.php
index 67da518f6e..83cb90e0d1 100644
--- a/wp-admin/user-new.php
+++ b/wp-admin/user-new.php
@@ -375,7 +375,7 @@ $new_user_ignore_pass = $creating && isset( $_POST['noconfirmation'] ) ? wp_unsl
 <table class="form-table">
 	<tr class="form-field form-required">
 		<th scope="row"><label for="user_login"><?php _e('Username'); ?> <span class="description"><?php _e('(required)'); ?></span></label></th>
-		<td><input name="user_login" type="text" id="user_login" value="<?php echo esc_attr( $new_user_login ); ?>" aria-required="true" autocapitalize="none" autocorrect="off" /></td>
+		<td><input name="user_login" type="text" id="user_login" value="<?php echo esc_attr( $new_user_login ); ?>" aria-required="true" autocapitalize="none" autocorrect="off" maxlength="60" /></td>
 	</tr>
 	<tr class="form-field form-required">
 		<th scope="row"><label for="email"><?php _e('Email'); ?> <span class="description"><?php _e('(required)'); ?></span></label></th>
diff --git a/wp-includes/user-functions.php b/wp-includes/user-functions.php
index e1b933e6cf..19f564344d 100644
--- a/wp-includes/user-functions.php
+++ b/wp-includes/user-functions.php
@@ -1245,19 +1245,28 @@ function wp_insert_user( $userdata ) {
 	//Remove any non-printable chars from the login string to see if we have ended up with an empty username
 	$user_login = trim( $pre_user_login );
 
+	// user_login must be between 0 and 60 characters.
 	if ( empty( $user_login ) ) {
 		return new WP_Error('empty_user_login', __('Cannot create a user with an empty login name.') );
+	} elseif ( mb_strlen( $user_login ) > 60 ) {
+		return new WP_Error( 'user_login_too_long', __( 'Username may not be longer than 60 characters.' ) );
 	}
+
 	if ( ! $update && username_exists( $user_login ) ) {
 		return new WP_Error( 'existing_user_login', __( 'Sorry, that username already exists!' ) );
 	}
 
-	// If a nicename is provided, remove unsafe user characters before
-	// using it. Otherwise build a nicename from the user_login.
+	/*
+	 * If a nicename is provided, remove unsafe user characters before using it.
+	 * Otherwise build a nicename from the user_login.
+	 */
 	if ( ! empty( $userdata['user_nicename'] ) ) {
 		$user_nicename = sanitize_user( $userdata['user_nicename'], true );
+		if ( mb_strlen( $user_nicename ) > 50 ) {
+			return new WP_Error( 'user_nicename_too_long', __( 'Nicename may not be longer than 50 characters.' ) );
+		}
 	} else {
-		$user_nicename = $user_login;
+		$user_nicename = mb_substr( $user_login, 0, 50 );
 	}
 
 	$user_nicename = sanitize_title( $user_nicename );
@@ -1395,7 +1404,9 @@ function wp_insert_user( $userdata ) {
 	if ( $user_nicename_check ) {
 		$suffix = 2;
 		while ($user_nicename_check) {
-			$alt_user_nicename = $user_nicename . "-$suffix";
+			// user_nicename allows 50 chars. Subtract one for a hyphen, plus the length of the suffix.
+			$base_length = 49 - mb_strlen( $suffix );
+			$alt_user_nicename = mb_substr( $user_nicename, 0, $base_length ) . "-$suffix";
 			$user_nicename_check = $wpdb->get_var( $wpdb->prepare("SELECT ID FROM $wpdb->users WHERE user_nicename = %s AND user_login != %s LIMIT 1" , $alt_user_nicename, $user_login));
 			$suffix++;
 		}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 83594613e5..3dfd825386 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34217';
+$wp_version = '4.4-alpha-34218';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.