diff --git a/phpBB/includes/acp/acp_attachments.php b/phpBB/includes/acp/acp_attachments.php
index 0961223002..fd71845660 100644
--- a/phpBB/includes/acp/acp_attachments.php
+++ b/phpBB/includes/acp/acp_attachments.php
@@ -225,7 +225,15 @@ class acp_attachments
 					if (in_array($config_name, array('attachment_quota', 'max_filesize', 'max_filesize_pm')))
 					{
 						$size_var = $request->variable($config_name, '');
-						$this->new_config[$config_name] = $config_value = ($size_var == 'kb') ? round($config_value * 1024) : (($size_var == 'mb') ? round($config_value * 1048576) : $config_value);
+
+						if (!empty($config_value))
+						{
+							$this->new_config[$config_name] = $config_value = ($size_var == 'kb') ? round($config_value * 1024) : (($size_var == 'mb') ? round($config_value * 1048576) : $config_value);
+						}
+						else
+						{
+							$config_value = 0;
+						}
 					}
 
 					if ($submit)