diff --git a/plugins/jspsych-webgazer-validate.js b/plugins/jspsych-webgazer-validate.js
index c014ae05..e25224a2 100644
--- a/plugins/jspsych-webgazer-validate.js
+++ b/plugins/jspsych-webgazer-validate.js
@@ -241,6 +241,9 @@
 
     function calculateSampleRate(gazeData){
       var mean_diff = [];
+      if(gazeData.length == 0){
+        return 0;
+      }
       for(var i=0; i<gazeData.length; i++){
         if(gazeData[i].length > 1){
           var t_diff = [];
@@ -255,7 +258,6 @@
       } else {
         return null;
       }
-      
     }
 
     function validation_done(){