diff --git a/lib/asn1.js b/lib/asn1.js
index dc94496..b08c3d5 100644
--- a/lib/asn1.js
+++ b/lib/asn1.js
@@ -313,7 +313,7 @@ const encodeBacnetDate = (buffer, value) => {
   } else {
     return;
   }
-  buffer.buffer[buffer.offset++] = value.getMonth();
+  buffer.buffer[buffer.offset++] = value.getMonth() + 1;
   buffer.buffer[buffer.offset++] = value.getDate();
   buffer.buffer[buffer.offset++] = (value.getDay() === 0) ? 7 : value.getDay();
 };