diff --git a/src/blocks/scratch3_sensing.js b/src/blocks/scratch3_sensing.js
index c56861d60..c940c5068 100644
--- a/src/blocks/scratch3_sensing.js
+++ b/src/blocks/scratch3_sensing.js
@@ -117,7 +117,7 @@ Scratch3SensingBlocks.prototype.getKeyPressed = function (args, util) {
 
 Scratch3SensingBlocks.prototype.daysSince2000 = function () {
     var msPerDay = 24 * 60 * 60 * 1000;
-    var start = new Date(2000, 1 - 1, 1);
+    var start = new Date(2000, 0, 1); // Months are 0-indexed.
     var today = new Date();
     var dstAdjust = today.getTimezoneOffset() - start.getTimezoneOffset();
     var mSecsSinceStart = today.valueOf() - start.valueOf();