diff --git a/src/App.tsx b/src/App.tsx
index 401fb8e..289f029 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,6 +1,6 @@
 import React, {FormEvent} from 'react';
 import {Calendar} from './Calendar';
-import {endGregorian, frSupportedYear, gregorianJDN, jdnFrench, Month, startGregorian} from './dates';
+import {endGregorian, endJD, frSupportedYear, gregorianJDN, jdnFrench, Month, startGregorian, startJD} from './dates';
 
 type YearMonth = {
     year: number;
@@ -92,7 +92,7 @@ class App extends React.Component<{}, AppState> {
             return;
 
         const jdn = gregorianJDN(+this.state.goYear, +this.state.goMonth, +this.state.goDay);
-        const {year, month} = jdnFrench(jdn);
+        const {year, month} = jdnFrench(Math.min(Math.max(startJD, jdn), endJD));
         this.setState({year, month});
     }
 
diff --git a/src/dates.ts b/src/dates.ts
index 0916dde..71ef10c 100644
--- a/src/dates.ts
+++ b/src/dates.ts
@@ -63,7 +63,7 @@ export const decadeNames = [
     'primidi', 'duodi', 'tridi', 'quartidi', 'quintidi', 'sextidi', 'septidi', 'octidi', 'nonidi', 'décadi',
 ];
 
-const startJD = data.start_jd;
+export const startJD = data.start_jd;
 export const startYear = data.start_year;
 const leaps: Array<number> = [0];
 
@@ -107,8 +107,9 @@ export function jdnGregorian(jdn: number): Date {
     return new Date(year, month - 1, day);
 }
 
+export const endJD = frJDN(endYear, 13, frIsLeap(endYear) ? 6: 5);
 export const startGregorian = jdnGregorian(startJD);
-export const endGregorian = jdnGregorian(frJDN(endYear, 13, frIsLeap(endYear) ? 6: 5));
+export const endGregorian = jdnGregorian(endJD);
 
 export function jdnFrench(jdn: number): FrenchDate {
     let lo = 0;