diff --git a/mlkem/src/verify.h b/mlkem/src/verify.h
index 600afa44a..0911a46b8 100644
--- a/mlkem/src/verify.h
+++ b/mlkem/src/verify.h
@@ -333,7 +333,7 @@ __contract__(
   ensures((return_value == 0) == forall(i, 0, len, (a[i] == b[i]))))
 {
   uint8_t r = 0, s = 0;
-  unsigned i;
+  size_t i;
 
   for (i = 0; i < len; i++)
   __loop__(