diff --git a/lib/converters/genericConverter.js b/lib/converters/genericConverter.js
index b1b8f37e4..3b39bb95f 100644
--- a/lib/converters/genericConverter.js
+++ b/lib/converters/genericConverter.js
@@ -13,7 +13,8 @@ exports.iobState2EntityState = function (entity, val, attribute) {
     } else if (typeof val === 'number' && entity.attributes && ['timestamp'].includes(entity.attributes.device_class)) {
         return val; //do not convert timestamps.
     } else if (typeof val === 'number' && entity.attributes && ['date'].includes(entity.attributes.device_class)) {
-        return new Date(val).toDateString(); //convert to date string
+        const dateStr = new Date(val).toDateString(); //convert to date string
+        return dateStr === 'Invalid Date' ? 'unknown' : dateStr;
     } else if (type === 'lock') {
         return val ? 'unlocked' : 'locked';
     } else if (typeof val === 'boolean' && type !== 'media_player') {