diff --git a/spacepackets/util.py b/spacepackets/util.py
index 3c3e46d..6c73db2 100644
--- a/spacepackets/util.py
+++ b/spacepackets/util.py
@@ -337,7 +337,7 @@ def from_int(byte_len: int, val: int) -> UnsignedByteField:
             return ByteFieldU32(val)
         elif byte_len == 8:
             return ByteFieldU64(val)
-        raise ValueError("invalid byte length")
+        raise ValueError(f"invalid byte length {byte_len}")
 
     @staticmethod
     def from_bytes(byte_len: int, stream: bytes) -> UnsignedByteField:
@@ -352,7 +352,7 @@ def from_bytes(byte_len: int, stream: bytes) -> UnsignedByteField:
             return ByteFieldU32.from_u32_bytes(stream)
         elif byte_len == 8:
             return ByteFieldU64.from_u64_bytes(stream)
-        raise ValueError("invalid byte length")
+        raise ValueError(f"invalid byte length {byte_len}")
 
 
 if __name__ == "__main__":
diff --git a/tests/test_countdown.py b/tests/test_countdown.py
index 6f09eb6..983637c 100644
--- a/tests/test_countdown.py
+++ b/tests/test_countdown.py
@@ -1,7 +1,7 @@
 import time
 from datetime import timedelta
 from unittest import TestCase
-from spacepackets.util import Countdown
+from spacepackets.countdown import Countdown
 
 
 class CountdownTest(TestCase):
diff --git a/tests/test_util.py b/tests/test_util.py
index 1f310df..0c5740f 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -85,6 +85,14 @@ def test_byte_field_u64_invalid_unpack(self):
         with self.assertRaises(ValueError):
             ByteFieldU64.from_u64_bytes(bytes([1, 2, 3, 4, 5]))
 
+    def test_byte_field_generator_invalid_unpack(self):
+        with self.assertRaises(ValueError):
+            ByteFieldGenerator.from_bytes(3, bytes([1, 2, 3, 4]))
+
+    def test_byte_field_generator_invalid_unpack_2(self):
+        with self.assertRaises(ValueError):
+            ByteFieldGenerator.from_int(3, 25)
+
     def test_two_byte_field_gen(self):
         two_byte_test = ByteFieldGenerator.from_int(byte_len=2, val=0x1842)
         self.assertEqual(ByteFieldU16(0x1842), two_byte_test)