diff --git a/frontend/src/hooks/useTrafficData.ts b/frontend/src/hooks/useTrafficData.ts
index bbd7b74ef6..f96c8cba01 100644
--- a/frontend/src/hooks/useTrafficData.ts
+++ b/frontend/src/hooks/useTrafficData.ts
@@ -47,6 +47,18 @@ const calculateTrafficDataCost = (trafficData: number) => {
 const padMonth = (month: number): string =>
     month < 10 ? `0${month}` : `${month}`;
 
+const safeLocaleString = (date: Date): string => {
+    try {
+        return date.toLocaleString('en-US', {
+            day: '2-digit',
+            month: '2-digit',
+            year: 'numeric',
+        });
+    } catch (e) {
+        console.error(`Invalid toLocaleString locale: en-US, date: ${date}`, e);
+        return '';
+    }
+};
 export const toSelectablePeriod = (
     date: Date,
     label?: string,
@@ -60,9 +72,7 @@ export const toSelectablePeriod = (
         year,
         month,
         dayCount,
-        label:
-            label ||
-            date.toLocaleString('en-US', { month: 'long', year: 'numeric' }),
+        label: label || safeLocaleString(date),
     };
 };
 
diff --git a/frontend/src/utils/formatDate.ts b/frontend/src/utils/formatDate.ts
index a8c073007c..65ac97cd8e 100644
--- a/frontend/src/utils/formatDate.ts
+++ b/frontend/src/utils/formatDate.ts
@@ -3,7 +3,7 @@ export const formatDateYMDHMS = (
     locale?: string,
 ): string => {
     try {
-        return new Date(date).toLocaleString(locale, {
+        return new Date(date).toLocaleString(locale ?? 'en-US', {
             day: '2-digit',
             month: '2-digit',
             year: 'numeric',
@@ -26,7 +26,7 @@ export const formatDateYMDHM = (
     timeZone?: string,
 ): string => {
     try {
-        return new Date(date).toLocaleString(locale, {
+        return new Date(date).toLocaleString(locale ?? 'en-US', {
             day: '2-digit',
             month: '2-digit',
             year: 'numeric',
@@ -49,7 +49,7 @@ export const formatDateYMD = (
     timeZone?: string,
 ): string => {
     try {
-        return new Date(date).toLocaleString(locale, {
+        return new Date(date).toLocaleString(locale ?? 'en-US', {
             day: '2-digit',
             month: '2-digit',
             year: 'numeric',
@@ -69,7 +69,7 @@ export const formatDateHM = (
     locale: string,
 ): string => {
     try {
-        return new Date(date).toLocaleString(locale, {
+        return new Date(date).toLocaleString(locale ?? 'en-US', {
             hour: '2-digit',
             minute: '2-digit',
         });