diff --git a/wp-admin/includes/ms.php b/wp-admin/includes/ms.php
index f72a51d69b..d00c847d68 100644
--- a/wp-admin/includes/ms.php
+++ b/wp-admin/includes/ms.php
@@ -385,9 +385,11 @@ function get_upload_space_available() {
  */
 function get_space_allowed() {
 	$space_allowed = get_option( 'blog_upload_space' );
-	if ( $space_allowed === false )
+
+	if ( ! is_numeric( $space_allowed ) )
 		$space_allowed = get_site_option( 'blog_upload_space' );
-	if ( empty( $space_allowed ) || !is_numeric( $space_allowed ) )
+
+	if ( ! is_numeric( $space_allowed ) )
 		$space_allowed = 50;
 
 	return $space_allowed;