diff --git a/xlsx.js b/xlsx.js
index ccbd3dd..2616f1b 100644
--- a/xlsx.js
+++ b/xlsx.js
@@ -3269,10 +3269,12 @@ function evert_arr(obj) {
 	return o;
 }
 
-var basedate = new Date(1899, 11, 30, 0, 0, 0); // 2209161600000
+var basedate = new Date(1899, 11, 31, 0, 0, 0); // 2209075200000
+var base1904 = new Date(1900, 2, 1, 0, 0, 0);
 function datenum(v, date1904) {
 	var epoch = v.getTime();
-	if(date1904) epoch -= 1462*24*60*60*1000;
+	if(date1904) epoch -= 1461*24*60*60*1000;
+	else if(v >= base1904) epoch += 24*60*60*1000;
 	var dnthresh = basedate.getTime() + (v.getTimezoneOffset() - basedate.getTimezoneOffset()) * 60000;
 	return (epoch - dnthresh) / (24 * 60 * 60 * 1000);
 }