diff --git a/vm/aging_space.hpp b/vm/aging_space.hpp
index c2ec2a645e..1fac4605d2 100644
--- a/vm/aging_space.hpp
+++ b/vm/aging_space.hpp
@@ -1,8 +1,20 @@
 namespace factor
 {
 
-struct aging_space : old_space {
-	aging_space(cell size, cell start) : old_space(size,start) {}
+struct aging_space : zone {
+	object_start_map starts;
+
+	aging_space(cell size, cell start) :
+		zone(size,start), starts(size,start) {}
+
+	object *allot(cell size)
+	{
+		if(here + size > end) return NULL;
+
+		object *obj = zone::allot(size);
+		starts.record_object_start_offset(obj);
+		return obj;
+	}
 };
 
 }
diff --git a/vm/code_heap.hpp b/vm/code_heap.hpp
index e98d966afe..b29e33ca64 100755
--- a/vm/code_heap.hpp
+++ b/vm/code_heap.hpp
@@ -6,11 +6,6 @@ struct code_heap_layout {
 	{
 		return block->size();
 	}
-
-	heap_block *next_block_after(heap_block *block)
-	{
-		return (heap_block *)((cell)block + block_size(block));
-	}
 };
 
 struct code_heap : heap<heap_block,code_heap_layout> {
diff --git a/vm/copying_collector.hpp b/vm/copying_collector.hpp
index dd36b680a6..4bb56945a1 100644
--- a/vm/copying_collector.hpp
+++ b/vm/copying_collector.hpp
@@ -95,7 +95,7 @@ struct copying_collector : collector<TargetGeneration,Policy> {
 
 						if(end < card_start_address(card_index))
 						{
-							start = gen->find_object_containing_card(card_index - gen_start_card);
+							start = gen->starts.find_object_containing_card(card_index - gen_start_card);
 							binary_start = start + this->parent->binary_payload_start((object *)start);
 							end = start + ((object *)start)->size();
 						}
diff --git a/vm/data_heap.hpp b/vm/data_heap.hpp
index c882262732..3a0af1f36a 100755
--- a/vm/data_heap.hpp
+++ b/vm/data_heap.hpp
@@ -52,7 +52,7 @@ template<typename Generation> void data_heap::reset_generation(Generation *gen)
 
 	clear_cards(gen);
 	clear_decks(gen);
-	gen->clear_object_start_offsets();
+	gen->starts.clear_object_start_offsets();
 }
 
 }
diff --git a/vm/heap.hpp b/vm/heap.hpp
index 653ac2d93d..c82b88ee2f 100644
--- a/vm/heap.hpp
+++ b/vm/heap.hpp
@@ -28,6 +28,11 @@ template<typename Block, typename HeapLayout> struct heap {
 		return (Block *)seg->end;
 	}
 
+	Block *next_block_after(heap_block *block)
+	{
+		return (Block *)((cell)block + layout.block_size(block));
+	}
+
 	void clear_free_list();
 	void add_to_free_list(free_heap_block *block);
 	void build_free_list(cell size);
@@ -50,7 +55,7 @@ template<typename Block, typename HeapLayout> struct heap {
 
 		while(scan != end)
 		{
-			Block *next = layout.next_block_after(scan);
+			Block *next = next_block_after(scan);
 			if(!scan->free_p()) iter(scan,layout.block_size(scan));
 			scan = next;
 		}
@@ -229,7 +234,7 @@ void heap<Block,HeapLayout>::heap_usage(cell *used, cell *total_free, cell *max_
 		else
 			*used += size;
 
-		scan = layout.next_block_after(scan);
+		scan = next_block_after(scan);
 	}
 }
 
@@ -243,7 +248,7 @@ cell heap<Block,HeapLayout>::heap_size()
 	while(scan != end)
 	{
 		if(scan->free_p()) break;
-		else scan = layout.next_block_after(scan);
+		else scan = next_block_after(scan);
 	}
 
 	if(scan != end)
@@ -308,7 +313,7 @@ void heap<Block,HeapLayout>::sweep_heap(Iterator &iter)
 			}
 		}
 
-		scan = layout.next_block_after(scan);
+		scan = next_block_after(scan);
 	}
 
 	if(prev && prev->free_p())
diff --git a/vm/image.cpp b/vm/image.cpp
index f41ae555a3..7d8c4a2d32 100755
--- a/vm/image.cpp
+++ b/vm/image.cpp
@@ -203,7 +203,7 @@ void factor_vm::relocate_data(cell data_relocation_base, cell code_relocation_ba
 	while(obj)
 	{
 		relocate_object((object *)obj,data_relocation_base,code_relocation_base);
-		data->tenured->record_object_start_offset((object *)obj);
+		data->tenured->starts.record_object_start_offset((object *)obj);
 		obj = data->tenured->next_object_after(obj);
 	}
 }
diff --git a/vm/layouts.hpp b/vm/layouts.hpp
index f0dbff6c30..ca51fd6dca 100644
--- a/vm/layouts.hpp
+++ b/vm/layouts.hpp
@@ -148,8 +148,17 @@ struct header {
 struct object {
 	NO_TYPE_CHECK;
 	header h;
-	cell *slots() { return (cell *)this; }
+
 	cell size();
+
+	cell *slots() { return (cell *)this; }
+
+	/* Only valid for objects in tenured space; must fast to free_heap_block
+	to do anything with it if its free */
+	bool free_p()
+	{
+		return h.value & 1 == 1;
+	}
 };
 
 /* Assembly code makes assumptions about the layout of this struct */
diff --git a/vm/mark_bits.hpp b/vm/mark_bits.hpp
index d9c9534edb..bc318524b4 100644
--- a/vm/mark_bits.hpp
+++ b/vm/mark_bits.hpp
@@ -70,10 +70,15 @@ template<typename Block, typename HeapLayout> struct mark_bits {
 		return (bits[pair.first] & ((u64)1 << pair.second)) != 0;
 	}
 
+	Block *next_block_after(Block *block)
+	{
+		return (Block *)((cell)block + layout.block_size(block));
+	}
+
 	void set_bitmap_range(u64 *bits, Block *address)
 	{
 		std::pair<cell,cell> start = bitmap_deref(address);
-		std::pair<cell,cell> end = bitmap_deref(layout.next_block_after(address));
+		std::pair<cell,cell> end = bitmap_deref(next_block_after(address));
 
 		u64 start_mask = ((u64)1 << start.second) - 1;
 		u64 end_mask = ((u64)1 << end.second) - 1;
diff --git a/vm/old_space.cpp b/vm/old_space.cpp
index 9440749e52..5f992e783e 100644
--- a/vm/old_space.cpp
+++ b/vm/old_space.cpp
@@ -3,23 +3,24 @@
 namespace factor
 {
 
-old_space::old_space(cell size_, cell start_) : zone(size_,start_)
+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_);
 }
 
-old_space::~old_space()
+object_start_map::~object_start_map()
 {
 	delete[] object_start_offsets;
 }
 
-cell old_space::first_object_in_card(cell card_index)
+cell object_start_map::first_object_in_card(cell card_index)
 {
 	return object_start_offsets[card_index];
 }
 
-cell old_space::find_object_containing_card(cell card_index)
+cell object_start_map::find_object_containing_card(cell card_index)
 {
 	if(card_index == 0)
 		return start;
@@ -41,34 +42,16 @@ cell old_space::find_object_containing_card(cell card_index)
 }
 
 /* we need to remember the first object allocated in the card */
-void old_space::record_object_start_offset(object *obj)
+void object_start_map::record_object_start_offset(object *obj)
 {
 	cell idx = addr_to_card((cell)obj - start);
-	if(object_start_offsets[idx] == card_starts_inside_object)
-		object_start_offsets[idx] = ((cell)obj & addr_card_mask);
+	card obj_start = ((cell)obj & addr_card_mask);
+	object_start_offsets[idx] = std::min(object_start_offsets[idx],obj_start);
 }
 
-object *old_space::allot(cell size)
-{
-	if(here + size > end) return NULL;
-
-	object *obj = zone::allot(size);
-	record_object_start_offset(obj);
-	return obj;
-}
-
-void old_space::clear_object_start_offsets()
+void object_start_map::clear_object_start_offsets()
 {
 	memset(object_start_offsets,card_starts_inside_object,addr_to_card(size));
 }
 
-cell old_space::next_object_after(cell scan)
-{
-	cell size = ((object *)scan)->size();
-	if(scan + size < here)
-		return scan + size;
-	else
-		return 0;
-}
-
 }
diff --git a/vm/old_space.hpp b/vm/old_space.hpp
index e59537cffb..640e205852 100644
--- a/vm/old_space.hpp
+++ b/vm/old_space.hpp
@@ -3,19 +3,18 @@ namespace factor
 
 static const cell card_starts_inside_object = 0xff;
 
-struct old_space : zone {
+struct object_start_map {
+	cell size, start;
 	card *object_start_offsets;
 	card *object_start_offsets_end;
 
-	old_space(cell size_, cell start_);
-	~old_space();
+	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);
-	object *allot(cell size);
 	void clear_object_start_offsets();
-	cell next_object_after(cell scan);
 };
 
 }
diff --git a/vm/tenured_space.hpp b/vm/tenured_space.hpp
index f9f584b200..a700b58bfd 100644
--- a/vm/tenured_space.hpp
+++ b/vm/tenured_space.hpp
@@ -1,8 +1,33 @@
 namespace factor
 {
 
-struct tenured_space : old_space {
-	tenured_space(cell size, cell start) : old_space(size,start) {}
+struct tenured_space_layout {
+	cell block_size(object *block)
+	{
+		if(block->free_p())
+		{
+			free_heap_block *free_block = (free_heap_block *)block;
+			return free_block->size();
+		}
+		else
+			return block->size();
+	}
+};
+
+struct tenured_space : zone {
+	object_start_map starts;
+
+	tenured_space(cell size, cell start) :
+		zone(size,start), starts(size,start) {}
+
+	object *allot(cell size)
+	{
+		if(here + size > end) return NULL;
+
+		object *obj = zone::allot(size);
+		starts.record_object_start_offset(obj);
+		return obj;
+	}
 };
 
 }
diff --git a/vm/zone.hpp b/vm/zone.hpp
index 2c28922fbc..42196f315b 100644
--- a/vm/zone.hpp
+++ b/vm/zone.hpp
@@ -21,6 +21,15 @@ struct zone {
 		here = h + align(size,data_alignment);
 		return (object *)h;
 	}
+
+	cell next_object_after(cell scan)
+	{
+		cell size = ((object *)scan)->size();
+		if(scan + size < here)
+			return scan + size;
+		else
+			return 0;
+	}
 };
 
 }