diff --git a/piwik-tracker/piwik-tracker-tests.ts b/piwik-tracker/piwik-tracker-tests.ts
index f509fe57e..7d06d6bdc 100644
--- a/piwik-tracker/piwik-tracker-tests.ts
+++ b/piwik-tracker/piwik-tracker-tests.ts
@@ -9,7 +9,7 @@ var PiwikTracker = require('piwik-tracker');
 var piwik = new PiwikTracker(1, 'http://mywebsite.com/piwik.php');
  
 // Optional: Respond to tracking errors 
-piwik.on('error', function(err) {
+piwik.on('error', function(err : Error) {
   console.log('error tracking request: ', err)
 })