diff --git a/lib/timespan.js b/lib/timespan.js
index e509869..b13a1ba 100644
--- a/lib/timespan.js
+++ b/lib/timespan.js
@@ -1,11 +1,13 @@
-var ms = require('ms');
+var ms = require('ms-tiny');
 
 module.exports = function (time, iat) {
   var timestamp = iat || Math.floor(Date.now() / 1000);
 
   if (typeof time === 'string') {
-    var milliseconds = ms(time);
-    if (typeof milliseconds === 'undefined') {
+    var milliseconds;
+    try {
+      milliseconds = ms(time);
+    } catch (e) {
       return;
     }
     return Math.floor(timestamp + milliseconds / 1000);
diff --git a/package.json b/package.json
index eab30c0..0c07f17 100644
--- a/package.json
+++ b/package.json
@@ -44,7 +44,7 @@
     "lodash.isplainobject": "^4.0.6",
     "lodash.isstring": "^4.0.1",
     "lodash.once": "^4.0.0",
-    "ms": "^2.1.1",
+    "ms-tiny": "^1.1.0",
     "semver": "^7.5.4"
   },
   "devDependencies": {
diff --git a/test/jwt.asymmetric_signing.tests.js b/test/jwt.asymmetric_signing.tests.js
index a8472d5..08064ef 100644
--- a/test/jwt.asymmetric_signing.tests.js
+++ b/test/jwt.asymmetric_signing.tests.js
@@ -5,7 +5,7 @@ const path = require('path');
 
 const expect = require('chai').expect;
 const assert = require('chai').assert;
-const ms = require('ms');
+const ms = require('ms-tiny');
 
 function loadKey(filename) {
   return fs.readFileSync(path.join(__dirname, filename));