diff --git wp-admin/includes/user.php wp-admin/includes/user.php
index 729ec18..c49c55b 100644
--- wp-admin/includes/user.php
+++ wp-admin/includes/user.php
@@ -104,9 +104,11 @@ function edit_user( $user_id = 0 ) {
 
 	$errors = new WP_Error();
 
-	/* checking that username has been typed */
+	/* checking that username has been typed and user_login is less than 50 characters */
 	if ( $user->user_login == '' )
 		$errors->add( 'user_login', __( '<strong>ERROR</strong>: Please enter a username.' ) );
+	elseif ( strlen( $user->user_login ) > 50 )
+		$errors->add( 'user_login', __( '<strong>ERROR</strong>: Please enter a username less than 50 characters.' ) );
 
 	/* checking the password has been typed twice */
 	/**
diff --git wp-admin/user-new.php wp-admin/user-new.php
index 2f6c5bf..8e71d4a 100644
--- wp-admin/user-new.php
+++ wp-admin/user-new.php
@@ -393,7 +393,7 @@ $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="50" /></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>