diff --git a/core/compiler/constants/constants.factor b/core/compiler/constants/constants.factor
index 9594cf7b23..8610f490ec 100755
--- a/core/compiler/constants/constants.factor
+++ b/core/compiler/constants/constants.factor
@@ -4,8 +4,8 @@ USING: math kernel layouts system ;
 IN: compiler.constants
 
 ! These constants must match vm/memory.h
-: card-bits 6 ;
-: deck-bits 12 ;
+: card-bits 8 ;
+: deck-bits 18 ;
 : card-mark HEX: 40 HEX: 80 bitor ;
 
 ! These constants must match vm/layouts.h
diff --git a/vm/data_gc.c b/vm/data_gc.c
index f44b8a7a05..c12c65aaff 100755
--- a/vm/data_gc.c
+++ b/vm/data_gc.c
@@ -59,6 +59,8 @@ F_DATA_HEAP *alloc_data_heap(CELL gens,
 		return NULL; /* can't happen */
 	}
 
+	total_size += DECK_SIZE;
+
 	data_heap->segment = alloc_segment(total_size);
 
 	data_heap->generations = safe_malloc(sizeof(F_ZONE) * data_heap->gen_count);
@@ -75,7 +77,7 @@ F_DATA_HEAP *alloc_data_heap(CELL gens,
 	data_heap->decks = safe_malloc(decks_size);
 	data_heap->decks_end = data_heap->decks + decks_size;
 
-	CELL alloter = data_heap->segment->start;
+	CELL alloter = (data_heap->segment->start + DECK_SIZE - 1) & ~(DECK_SIZE - 1);
 
 	alloter = init_zone(&data_heap->generations[TENURED],tenured_size,alloter);
 	alloter = init_zone(&data_heap->semispaces[TENURED],tenured_size,alloter);
@@ -92,7 +94,7 @@ F_DATA_HEAP *alloc_data_heap(CELL gens,
 		alloter = init_zone(&data_heap->semispaces[NURSERY],0,alloter);
 	}
 
-	if(alloter != data_heap->segment->end)
+	if(data_heap->segment->end - alloter > DECK_SIZE)
 		critical_error("Bug in alloc_data_heap",alloter);
 
 	return data_heap;
@@ -163,6 +165,10 @@ void gc_reset(void)
 	int i;
 	for(i = 0; i < MAX_GEN_COUNT; i++)
 		memset(&gc_stats[i],0,sizeof(F_GC_STATS));
+
+	cards_scanned = 0;
+	decks_scanned = 0;
+	code_heap_scans = 0;
 }
 
 void init_data_heap(CELL gens,
@@ -182,10 +188,6 @@ void init_data_heap(CELL gens,
 	secure_gc = secure_gc_;
 
 	gc_reset();
-
-	cards_scanned = 0;
-	decks_scanned = 0;
-	code_heap_scans = 0;
 }
 
 /* Size of the object pointed to by a tagged pointer */
diff --git a/vm/data_gc.h b/vm/data_gc.h
index 20692c14e6..301821bb7a 100755
--- a/vm/data_gc.h
+++ b/vm/data_gc.h
@@ -68,13 +68,11 @@ the offset of the first object is set by the allocator. */
 #define CARD_POINTS_TO_NURSERY 0x80
 #define CARD_POINTS_TO_AGING 0x40
 #define CARD_MARK_MASK (CARD_POINTS_TO_NURSERY | CARD_POINTS_TO_AGING)
-#define CARD_BASE_MASK 0x3f
+#define CARD_BASE_MASK 0xff
 typedef u8 F_CARD;
 
-/* A card is 64 bytes. 6 bits is sufficient to represent every
-offset within the card */
-#define CARD_SIZE 64
-#define CARD_BITS 6
+#define CARD_BITS 8
+#define CARD_SIZE (1<<CARD_BITS)
 #define ADDR_CARD_MASK (CARD_SIZE-1)
 
 DLLEXPORT CELL cards_offset;
@@ -83,11 +81,10 @@ DLLEXPORT CELL allot_markers_offset;
 #define ADDR_TO_CARD(a) (F_CARD*)(((CELL)(a) >> CARD_BITS) + cards_offset)
 #define CARD_TO_ADDR(c) (CELL*)(((CELL)(c) - cards_offset)<<CARD_BITS)
 
-/* A deck is 4 kilobytes or 64 cards. */
 typedef u8 F_DECK;
 
-#define DECK_SIZE (4 * 1024)
-#define DECK_BITS 12
+#define DECK_BITS (CARD_BITS + 10)
+#define DECK_SIZE (1<<DECK_BITS)
 #define ADDR_DECK_MASK (DECK_SIZE-1)
 
 DLLEXPORT CELL decks_offset;