diff --git a/generate/derivation/verify.py b/generate/derivation/verify.py
index fa579dcd..71f187c0 100644
--- a/generate/derivation/verify.py
+++ b/generate/derivation/verify.py
@@ -30,6 +30,7 @@ from typing import Final
 # Canonical grounding primitives — reused so this gate stays identical to the
 # round-trip filter's notion of "appears in the problem text".
 from generate.math_roundtrip import _token_in, _tokens, _value_grounds
+from collections import Counter
 from generate.derivation.extract import extract_quantities
 from generate.derivation.model import GroundedDerivation