diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index bf2f2c1..3c8bf60 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -6355,10 +6355,12 @@ int moo_execute (moo_t* moo)
 
 	moo->proc_switched = 0;
 	moo->abort_req = 0;
+	moo->gci.lazy_sweep = 1; /* TODO: make it configurable?? */
 
-//moo->gci.lazy_sweep = 1;
 	n = __execute (moo);
 
+	moo->gci.lazy_sweep = 0;
+
 	vm_cleanup (moo);
 
 	moo->log.default_type_mask = log_default_type_mask;
diff --git a/moo/lib/gc.c b/moo/lib/gc.c
index 4fff5fc..c0eace3 100644
--- a/moo/lib/gc.c
+++ b/moo/lib/gc.c
@@ -1003,7 +1003,6 @@ void moo_gc_ms_sweep_lazy (moo_t* moo, moo_oow_t allocsize)
 
 	freed_size = 0;
 
-//printf ("starting lazy sweep...gci.ls.curr [%p]\n", moo->gci.ls.curr);
 	prev = moo->gci.ls.prev;
 	curr = moo->gci.ls.curr;
 
@@ -1031,10 +1030,8 @@ void moo_gc_ms_sweep_lazy (moo_t* moo, moo_oow_t allocsize)
 
 			if (freed_size > allocsize)  /* TODO: can it secure large enough space? */
 			{
-//printf ("stopping lazy sweeping after %lu free, allocsize %lu\n", (unsigned long int)freed_size, (unsigned long int)allocsize);
-				moo->gci.ls.curr = next; /* let the next lazy sweeping begin at this point */
 				moo->gci.ls.prev = prev;
-//printf ("finished lazy sweep...\n");
+				moo->gci.ls.curr = next; /* let the next lazy sweeping begin at this point */
 				return;
 			}
 		}
@@ -1043,7 +1040,6 @@ void moo_gc_ms_sweep_lazy (moo_t* moo, moo_oow_t allocsize)
 	}
 
 	moo->gci.ls.curr = MOO_NULL;
-//printf ("finished lazy sweep...\n");
 }
 
 static MOO_INLINE void gc_ms_sweep (moo_t* moo)
@@ -1075,7 +1071,6 @@ static MOO_INLINE void gc_ms_sweep (moo_t* moo)
 		curr = next;
 	}
 
-printf ("finised full sweep...\n");
 	moo->gci.ls.curr = MOO_NULL;
 }
 #endif
@@ -1397,6 +1392,8 @@ void moo_gc (moo_t* moo, int full)
 #if defined(MOO_ENABLE_GC_MARK_SWEEP)
 	if (moo->gc_type == MOO_GC_TYPE_MARK_SWEEP)
 	{
+if (moo->gci.lazy_sweep) moo_gc_ms_sweep_lazy (moo, MOO_TYPE_MAX(moo_oow_t));
+
 		MOO_LOG1 (moo, MOO_LOG_GC | MOO_LOG_INFO, "Starting GC (mark-sweep) - gci.bsz = %zu\n", moo->gci.bsz);
 
 		moo->gci.stack.len = 0;
@@ -1405,6 +1402,9 @@ void moo_gc (moo_t* moo, int full)
 
 		if (!full && moo->gci.lazy_sweep) 
 		{
+			/* set the lazy sweeping point to the head of the allocated blocks.
+			 * hawk_allocbytes() updates moo->gci.ls.prev if it is called while
+			 * moo->gci.ls.curr stays at moo->gci.b */
 			moo->gci.ls.prev = MOO_NULL;
 			moo->gci.ls.curr = moo->gci.b;
 		}
diff --git a/moo/lib/obj.c b/moo/lib/obj.c
index ea47319..b2ccf3c 100644
--- a/moo/lib/obj.c
+++ b/moo/lib/obj.c
@@ -79,6 +79,14 @@ void* moo_allocbytes (moo_t* moo, moo_oow_t size)
 			}
 		}
 
+		if (moo->gci.lazy_sweep && moo->gci.ls.curr == moo->gci.b) 
+		{
+			/* if the lazy sweeping point is at the beginning of the allocation block,
+			 * moo->gc.ls.prev must get updated */
+			MOO_ASSERT (moo, moo->gci.ls.prev == MOO_NULL);
+			moo->gci.ls.prev = gch;
+		}
+
 		gch->next = moo->gci.b;
 		moo->gci.b = gch;
 		moo->gci.bsz += size;
diff --git a/moo/lib/xma.c b/moo/lib/xma.c
index 34c37c0..1a9237e 100644
--- a/moo/lib/xma.c
+++ b/moo/lib/xma.c
@@ -236,6 +236,12 @@ int moo_xma_init (moo_xma_t* xma, moo_mmgr_t* mmgr, void* zoneptr, moo_oow_t zon
 
 		internal = 1; /* internally created. must be freed upon moo_xma_fini() */
 	}
+	else if (zonesize < FBLKMINSIZE) 
+	{
+		/* the zone size is too small for an externally allocated zone. */
+/* TODO: difference error code from memory allocation failure.. this is not really memory shortage */
+		return -1;
+	}
 
 	first = (moo_xma_fblk_t*)zoneptr;