diff --git a/vm/arrays.hpp b/vm/arrays.hpp
index 48be881230..6063269e7f 100755
--- a/vm/arrays.hpp
+++ b/vm/arrays.hpp
@@ -15,7 +15,6 @@ inline void factor_vm::set_array_nth(array *array, cell slot, cell value)
 #ifdef FACTOR_DEBUG
 	assert(slot < array_capacity(array));
 	assert(array->h.hi_tag() == ARRAY_TYPE);
-	check_tagged_pointer(value);
 #endif
 	cell *slot_ptr = &array->data()[slot];
 	*slot_ptr = value;
diff --git a/vm/free_list_allocator.hpp b/vm/free_list_allocator.hpp
index efdad508cb..8332399279 100644
--- a/vm/free_list_allocator.hpp
+++ b/vm/free_list_allocator.hpp
@@ -22,7 +22,7 @@ template<typename Block> struct free_list_allocator {
 	Block *next_block_after(Block *block);
 	void clear_free_list();
 	void add_to_free_list(free_heap_block *block);
-	void build_free_list(cell size);
+	void initial_free_list(cell size);
 	void assert_free_block(free_heap_block *block);
 	free_heap_block *find_free_block(cell size);
 	free_heap_block *split_free_block(free_heap_block *block, cell size);
@@ -40,7 +40,7 @@ template<typename Block>
 free_list_allocator<Block>::free_list_allocator(cell size_, cell start_) :
 	size(size_), start(start_), end(start_ + size_), state(mark_bits<Block>(size_,start_))
 {
-	clear_free_list();
+	initial_free_list(0);
 }
 
 template<typename Block> void free_list_allocator<Block>::clear_free_list()
@@ -85,7 +85,7 @@ template<typename Block> void free_list_allocator<Block>::add_to_free_list(free_
 
 /* Called after reading the heap from the image file, and after heap compaction.
 Makes a free list consisting of one free block, at the very end. */
-template<typename Block> void free_list_allocator<Block>::build_free_list(cell size)
+template<typename Block> void free_list_allocator<Block>::initial_free_list(cell size)
 {
 	clear_free_list();
 	if(size != this->size)
@@ -345,7 +345,7 @@ void free_list_allocator<Block>::compact(Iterator &iter)
 
 	/* Now update the free list; there will be a single free block at
 	the end */
-	this->build_free_list((cell)compactor.address - this->start);
+	this->initial_free_list((cell)compactor.address - this->start);
 }
 
 template<typename Block>
diff --git a/vm/gc.cpp b/vm/gc.cpp
index 706831136b..6b3ec80481 100755
--- a/vm/gc.cpp
+++ b/vm/gc.cpp
@@ -60,12 +60,12 @@ void factor_vm::gc(gc_op op,
 			current_gc->op = collect_growing_heap_op;
 			break;
 		default:
-			critical_error("Bad GC op\n",op);
+			critical_error("Bad GC op",current_gc->op);
 			break;
 		}
 
 		if(verbosegc)
-			std::cout << "GC rewind, op=" << op << std::endl;
+			std::cout << "GC rewind, op=" << current_gc->op << std::endl;
 	}
 
 	switch(current_gc->op)
@@ -91,20 +91,20 @@ void factor_vm::gc(gc_op op,
 		record_gc_stats(&gc_stats.full_stats);
 		break;
 	default:
-		critical_error("Bad GC op\n",op);
+		critical_error("Bad GC op\n",current_gc->op);
 		break;
 	}
 
+	if(verbosegc)
+		std::cout << "GC done, op=" << current_gc->op << std::endl;
+
 	delete current_gc;
 	current_gc = NULL;
-
-	if(verbosegc)
-		std::cout << "GC done, op=" << op << std::endl;
 }
 
 void factor_vm::primitive_minor_gc()
 {
-	gc(collect_full_op,
+	gc(collect_nursery_op,
 		0, /* requested size */
 		true, /* trace contexts? */
 		false /* compact code heap? */);
diff --git a/vm/image.cpp b/vm/image.cpp
index 845ca6c1bc..f5879e7a32 100755
--- a/vm/image.cpp
+++ b/vm/image.cpp
@@ -36,7 +36,7 @@ void factor_vm::load_data_heap(FILE *file, image_header *h, vm_parameters *p)
 		fatal_error("load_data_heap failed",0);
 	}
 
-	data->tenured->build_free_list(h->data_size);
+	data->tenured->initial_free_list(h->data_size);
 }
 
 void factor_vm::load_code_heap(FILE *file, image_header *h, vm_parameters *p)
@@ -57,7 +57,7 @@ void factor_vm::load_code_heap(FILE *file, image_header *h, vm_parameters *p)
 		}
 	}
 
-	code->allocator->build_free_list(h->code_size);
+	code->allocator->initial_free_list(h->code_size);
 }
 
 void factor_vm::data_fixup(cell *handle, cell data_relocation_base)
diff --git a/vm/local_roots.hpp b/vm/local_roots.hpp
index 6ae059f4c4..58142be8f2 100644
--- a/vm/local_roots.hpp
+++ b/vm/local_roots.hpp
@@ -6,7 +6,7 @@ struct gc_root : public tagged<Type>
 {
 	factor_vm *parent;
 
-	void push() { parent->check_tagged_pointer(tagged<Type>::value()); parent->gc_locals.push_back((cell)this); }
+	void push() { parent->gc_locals.push_back((cell)this); }
 	
 	explicit gc_root(cell value_,factor_vm *vm) : tagged<Type>(value_),parent(vm) { push(); }
 	explicit gc_root(Type *value_, factor_vm *vm) : tagged<Type>(value_),parent(vm) { push(); }
diff --git a/vm/mark_bits.hpp b/vm/mark_bits.hpp
index 161a7fd755..279c04a23a 100644
--- a/vm/mark_bits.hpp
+++ b/vm/mark_bits.hpp
@@ -81,12 +81,21 @@ template<typename Block> struct mark_bits {
 			bits[start.first] |= start_mask ^ end_mask;
 		else
 		{
+#ifdef FACTOR_DEBUG
+			assert(start.first < bits_size);
+#endif
 			bits[start.first] |= ~start_mask;
 
 			for(cell index = start.first + 1; index < end.first; index++)
 				bits[index] = (u64)-1;
 
-			bits[end.first] |= end_mask;
+			if(end_mask != 0)
+			{
+#ifdef FACTOR_DEBUG
+				assert(end.first < bits_size);
+#endif
+				bits[end.first] |= end_mask;
+			}
 		}
 	}
 
diff --git a/vm/vm.hpp b/vm/vm.hpp
index 86ed092ff7..40dcb4f3bc 100755
--- a/vm/vm.hpp
+++ b/vm/vm.hpp
@@ -280,18 +280,6 @@ struct factor_vm
 	#endif
 	}
 
-	inline void check_tagged_pointer(cell tagged)
-	{
-	#ifdef FACTOR_DEBUG
-		if(!immediate_p(tagged))
-		{
-			object *obj = untag<object>(tagged);
-			check_data_pointer(obj);
-			obj->h.hi_tag();
-		}
-	#endif
-	}
-
 	// generic arrays
 	template<typename Array> Array *allot_uninitialized_array(cell capacity);
 	template<typename Array> bool reallot_array_in_place_p(Array *array, cell capacity);