diff --git a/racket/src/racket/gc2/mem_account.c b/racket/src/racket/gc2/mem_account.c
index 1f1565a2a7..abf104b406 100644
--- a/racket/src/racket/gc2/mem_account.c
+++ b/racket/src/racket/gc2/mem_account.c
@@ -371,8 +371,8 @@ int BTC_bi_chan_mark(void *p, struct NewGC *gc)
     /* Race conditions here on `mem_size', and likely double counting
        when the same async channels are accessible from paired bi
        channels --- but those approximations are ok for accounting. */
-    account_memory(gc, gc->current_mark_owner, bc->link->sendch->mem_size, 0);
-    account_memory(gc, gc->current_mark_owner, bc->link->recvch->mem_size, 0);
+    account_memory(gc, gc->current_mark_owner, gcBYTES_TO_WORDS(bc->link->sendch->mem_size), 0);
+    account_memory(gc, gc->current_mark_owner, gcBYTES_TO_WORDS(bc->link->recvch->mem_size), 0);
   }
   return gc->mark_table[btc_redirect_bi_chan](p, gc);
 }