diff --git a/lib/sandbox.js b/lib/sandbox.js
index 45d7e0669..82a8878a2 100644
--- a/lib/sandbox.js
+++ b/lib/sandbox.js
@@ -3392,6 +3392,8 @@ function sandBox(script, name, verbose, debug, context) {
             const minute = 60 * second;
             const hour = 60 * minute;
             const day = 24 * hour;
+            const neg = diff < 0;
+            diff = Math.abs(diff);
 
             if (/DD|TT|ДД|D|T|Д/.test(text)) {
                 const days = Math.floor(diff / day);
@@ -3439,7 +3441,7 @@ function sandBox(script, name, verbose, debug, context) {
 
             sandbox.verbose && sandbox.log(`formatTimeDiff(format=${format}, text=${text})`, 'debug');
 
-            return text;
+            return neg ? `-${text}` : text;
         },
         getDateObject: function (date) {
             if (isObject(date)) {