diff --git a/pylgbst/utilities.py b/pylgbst/utilities.py
index 4031576..0f5a7fe 100644
--- a/pylgbst/utilities.py
+++ b/pylgbst/utilities.py
@@ -20,13 +20,8 @@ queue = queue  # just to use it
 def check_unpack(seq, index, pattern, size):
     """Check that we got size bytes, if so, unpack using pattern"""
     data = seq[index: index + size]
-    if len(data) == size:
-        return unpack(pattern, data)[0]
-    else:
-        log.warning(
-            "Unpacking of %s bytes failed, insufficient data: %r", size, seq[index:]
-        )
-        raise ValueError(data, "Expected %s bytes" % (size,))
+    assert len(data) == size, "Unexpected data len %d, expected %d" % (len(data), size)
+    return unpack(pattern, data)[0]
 
 
 def usbyte(seq, index):