diff --git a/gc.c b/gc.c
index cf2704c0..228889e8 100644
--- a/gc.c
+++ b/gc.c
@@ -1417,8 +1417,11 @@ void gc_collector()
   //sweep : 
 
   for (heap_type = 0; heap_type < NUM_HEAP_TYPES; heap_type++) {
-    gc_sweep(gc_get_heap()->heap[heap_type], heap_type, &freed_tmp);
-    freed += freed_tmp;
+    gc_heap *h = gc_get_heap()->heap[heap_type];
+    if (h) {
+      gc_sweep(h, heap_type, &freed_tmp);
+      freed += freed_tmp;
+    }
   }
 
   // TODO: this loop only includes smallest 2 heaps, is that sufficient??
diff --git a/runtime.c b/runtime.c
index 78210cd1..6d2f7ddb 100644
--- a/runtime.c
+++ b/runtime.c
@@ -262,8 +262,8 @@ static bool set_insert(ck_hs_t * hs, const void *value)
 void gc_init_heap(long heap_size)
 {
   size_t initial_heap_size = INITIAL_HEAP_SIZE;
-  Cyc_heap = malloc(sizeof(gc_heap_root));
-  Cyc_heap->heap = malloc(sizeof(gc_heap *) * NUM_HEAP_TYPES);
+  Cyc_heap = calloc(1, sizeof(gc_heap_root));
+  Cyc_heap->heap = calloc(1, sizeof(gc_heap *) * NUM_HEAP_TYPES);
   Cyc_heap->heap[HEAP_REST] = gc_heap_create(HEAP_REST, initial_heap_size, 0, 0);
   Cyc_heap->heap[HEAP_SM] = gc_heap_create(HEAP_SM, initial_heap_size, 0, 0);
   Cyc_heap->heap[HEAP_64] = gc_heap_create(HEAP_64, initial_heap_size, 0, 0);