diff --git a/includes/core/class-files.php b/includes/core/class-files.php
index 39932ad5..7317fc6d 100644
--- a/includes/core/class-files.php
+++ b/includes/core/class-files.php
@@ -1133,14 +1133,16 @@ if ( ! class_exists( 'um\core\Files' ) ) {
 		 * @return string
 		 */
 		function format_bytes( $size , $precision = 1 ) {
+			if ( is_numeric( $size ) ) {
+				$base = log( $size, 1024 );
+				$suffixes = array( '', 'kb', 'MB', 'GB', 'TB' );
+				$computed_size = round( pow( 1024, $base - floor( $base ) ), $precision );
+				$unit = $suffixes[ floor( $base ) ];
 
-			$base = log($size, 1024);
-			$suffixes = array('', 'kb', 'MB', 'GB', 'TB');
-			$computed_size = round(pow(1024, $base - floor($base)), $precision);
-			$unit = $suffixes[ floor($base) ];
-
-			return   $computed_size.' '.$unit;
+				return $computed_size.' '.$unit;
+			}
 
+			return '';
 		}