diff --git a/jcal/src/Calendar.tsx b/jcal/src/Calendar.tsx
index 96931db..9b820ec 100644
--- a/jcal/src/Calendar.tsx
+++ b/jcal/src/Calendar.tsx
@@ -1,6 +1,6 @@
 import React from 'react';
 import './Calendar.scss';
-import {formatJG, jdnGregorian, JulianDay, JulianMonth, monthName, weekdayNames} from '@common/gregorian';
+import {formatJG, jdnGregorian, JulianDay, JulianMonth, monthName, jdnWeekDay, weekdayNames} from '@common/gregorian';
 import {jdnLongCount} from '@common/longCount';
 import {jdnJulian, julianJDN, julianMonthDays} from '@common/julian';
 import {frDateFormat, frEndJD, frStartJD, jdnFrench} from '@common/french';
@@ -46,7 +46,7 @@ function Day({year, month, day, todayJDN}: DateProps & { todayJDN: number }): JS
     const jdn = julianJDN(year, month, day);
     return <div className={`Day NormalDay ${jdn === todayJDN ? 'Day-today' : ''}`}>
         <div className="Day-name">{day}</div>
-        <div className="Day-weekday">{weekdayNames[(jdn + 1) % 7]}</div>
+        <div className="Day-weekday">{weekdayNames[jdnWeekDay(jdn)]}</div>
         <DayDetail jdn={jdn}/>
     </div>;
 }
@@ -54,7 +54,7 @@ function Day({year, month, day, todayJDN}: DateProps & { todayJDN: number }): JS
 function Month({year, month, todayJDN}: MonthProps & { todayJDN: number }): JSX.Element {
     const decadeHeads = weekdayNames.map((name, i) => <WeekdayName key={i} name={name}/>);
     const firstJDN = julianJDN(year, month, 1);
-    const firstWeekday = (firstJDN % 7 + 8) % 7;
+    const firstWeekday = jdnWeekDay(firstJDN);
     const daysTotal = julianMonthDays(year, month);
     return <div className="Month">
         <div className="Month-weekdayHead">{decadeHeads}</div>