diff --git a/adafruit_ntp.py b/adafruit_ntp.py
index bc6db0d..5d71a72 100644
--- a/adafruit_ntp.py
+++ b/adafruit_ntp.py
@@ -102,6 +102,10 @@ def datetime(self) -> time.struct_time:
             self.next_sync = destination + cache_offset * 1_000_000_000
             seconds = struct.unpack_from("!I", self._packet, offset=PACKET_SIZE - 8)[0]
 
+            # value should always be larger; giving a small buffer to handle jitter.
+            if seconds == 0:
+                raise ArithmeticError("ntp value is invalid (empty)")
+
             self._monotonic_start = (
                 seconds
                 + self._tz_offset