diff --git a/vm/collector.hpp b/vm/collector.hpp
index a8fab5e561..626ae2b6b5 100644
--- a/vm/collector.hpp
+++ b/vm/collector.hpp
@@ -99,18 +99,6 @@ template <typename TargetGeneration, typename Policy> struct collector {
     }
   }
 
-  cell first_card_in_deck(cell deck) {
-    return deck << (deck_bits - card_bits);
-  }
-
-  cell last_card_in_deck(cell deck) {
-    return first_card_in_deck(deck + 1);
-  }
-
-  cell card_deck_for_address(cell a) {
-    return addr_to_deck(a - data->start);
-  }
-
   void trace_partial_objects(cell start, cell card_start, cell card_end) {
     object* obj = (object*)start;
     cell end = start + obj->binary_payload_start();
@@ -160,8 +148,8 @@ template <typename TargetGeneration, typename Policy> struct collector {
     card_deck* decks = data->decks;
     card_deck* cards = data->cards;
 
-    cell first_deck = card_deck_for_address(gen->start);
-    cell last_deck = card_deck_for_address(gen->end);
+    cell first_deck = (gen->start - data->start) / deck_size;
+    cell last_deck = (gen->end - data->start) / deck_size;
 
     /* Address of last traced object. */
     cell start = 0;
@@ -171,8 +159,8 @@ template <typename TargetGeneration, typename Policy> struct collector {
         decks[deck_index] &= ~unmask;
         decks_scanned++;
 
-        cell first_card = first_card_in_deck(deck_index);
-        cell last_card = last_card_in_deck(deck_index);
+        cell first_card = cards_per_deck * deck_index;
+        cell last_card = first_card + cards_per_deck;
 
         for (cell card_index = first_card; card_index < last_card;
              card_index++) {
diff --git a/vm/data_heap.cpp b/vm/data_heap.cpp
index e483bb8938..7684c81877 100644
--- a/vm/data_heap.cpp
+++ b/vm/data_heap.cpp
@@ -23,12 +23,12 @@ data_heap::data_heap(bump_allocator* vm_nursery,
   cell total_size = young_size + 2 * aging_size + tenured_size + deck_size;
   seg = new segment(total_size, false);
 
-  cell cards_size = addr_to_card(total_size);
+  cell cards_size = total_size / card_size;
   cards = new card[cards_size];
   cards_end = cards + cards_size;
   memset(cards, 0, cards_size);
 
-  cell decks_size = addr_to_deck(total_size);
+  cell decks_size = total_size / deck_size;
   decks = new card_deck[decks_size];
   decks_end = decks + decks_size;
   memset(decks, 0, decks_size);
@@ -102,8 +102,8 @@ bool data_heap::low_memory_p() {
 }
 
 void data_heap::mark_all_cards() {
-  memset(cards, -1, cards_end - cards);
-  memset(decks, -1, decks_end - decks);
+  memset(cards, 0xff, cards_end - cards);
+  memset(decks, 0xff, decks_end - decks);
 }
 
 void factor_vm::set_data_heap(data_heap* data_) {
diff --git a/vm/object_start_map.cpp b/vm/object_start_map.cpp
index 78da247ea7..0b615d219b 100644
--- a/vm/object_start_map.cpp
+++ b/vm/object_start_map.cpp
@@ -4,30 +4,26 @@ namespace factor {
 
 object_start_map::object_start_map(cell size, cell start)
     : size(size), start(start) {
-  object_start_offsets = new card[addr_to_card(size)];
-  object_start_offsets_end = object_start_offsets + addr_to_card(size);
+  cell card_count = size / card_size;
+  object_start_offsets = new card[card_count];
+  object_start_offsets_end = object_start_offsets + card_count;
   clear_object_start_offsets();
 }
 
 object_start_map::~object_start_map() { delete[] object_start_offsets; }
 
-cell object_start_map::first_object_in_card(cell card_index) {
-  return object_start_offsets[card_index];
-}
-
 cell object_start_map::find_object_containing_card(cell card_index) {
   if (card_index == 0)
     return start;
   else {
     card_index--;
 
-    while (first_object_in_card(card_index) == card_starts_inside_object) {
+    while (object_start_offsets[card_index] == card_starts_inside_object) {
       /* First card should start with an object */
       FACTOR_ASSERT(card_index > 0);
       card_index--;
     }
-
-    return start + (card_index << card_bits) + first_object_in_card(card_index);
+    return start + card_index * card_size + object_start_offsets[card_index];
   }
 }
 
diff --git a/vm/object_start_map.hpp b/vm/object_start_map.hpp
index f916c8c041..c05dba6a64 100644
--- a/vm/object_start_map.hpp
+++ b/vm/object_start_map.hpp
@@ -10,7 +10,6 @@ struct object_start_map {
   object_start_map(cell size, cell start);
   ~object_start_map();
 
-  cell first_object_in_card(cell card_index);
   cell find_object_containing_card(cell card_index);
   void record_object_start_offset(object* obj);
   void clear_object_start_offsets();
diff --git a/vm/write_barrier.hpp b/vm/write_barrier.hpp
index d12c5f8164..d2382c755c 100644
--- a/vm/write_barrier.hpp
+++ b/vm/write_barrier.hpp
@@ -16,14 +16,16 @@ static const cell card_mark_mask =
 typedef uint8_t card;
 
 static const cell card_bits = 8;
-static const cell card_size = (1 << card_bits);
-static const cell addr_card_mask = (card_size - 1);
+static const cell card_size = 1 << card_bits;
+static const cell addr_card_mask = card_size - 1;
 
 typedef uint8_t card_deck;
 
-static const cell deck_bits = (card_bits + 10);
-static const cell deck_size = (1 << deck_bits);
-static const cell addr_deck_mask = (deck_size - 1);
+static const cell deck_bits = card_bits + 10;
+/* Number of bytes on the heap a deck addresses. Each deck as 1024
+   cards. So 256 kb. */
+static const cell deck_size = 1 << deck_bits;
+static const cell cards_per_deck = 1 << 10;
 
 inline cell addr_to_card(cell a) { return a >> card_bits; }