diff --git a/sw/decoders/utility.py b/sw/decoders/utility.py
index 06ae46c..8caf553 100644
--- a/sw/decoders/utility.py
+++ b/sw/decoders/utility.py
@@ -85,7 +85,7 @@ def test_decoder(encoder: typing.Any,
             y_hat = decoder.decode(y)
 
             total_bit_errors += count_bit_errors(d, y_hat)
-            total_bits += x.size
+            total_bits += d.size
 
             if total_bit_errors >= target_bit_errors:
                 break