diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 4b6ee750..2736c80a 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -708,10 +708,11 @@ gc_sweep_symbols(pic_state *pic)
   }
 }
 
-static void
+static size_t
 gc_sweep_page(pic_state *pic, struct heap_page *page)
 {
   union header *bp, *p, *head = NULL, *tail = NULL;
+  size_t alive = 0;
 
   for (bp = page->basep; ; bp = bp->s.ptr) {
     p = bp + (bp->s.size ? bp->s.size : 1); /* first bp's size is 0, so force advnce */
@@ -721,6 +722,7 @@ gc_sweep_page(pic_state *pic, struct heap_page *page)
       }
       if (gc_is_marked(p)) {
         gc_unmark(p);
+        alive += p->s.size;
       } else {
         if (head == NULL) {
           head = p;
@@ -741,14 +743,17 @@ gc_sweep_page(pic_state *pic, struct heap_page *page)
     gc_finalize_object(pic, (struct pic_object *)(p + 1));
     heap_free(pic, p + 1);
   }
+
+  return alive;
 }
 
 static void
 gc_sweep_phase(pic_state *pic)
 {
-  struct heap_page *page = pic->heap->pages;
+  struct heap_page *page;
   khiter_t it;
   khash_t(reg) *h;
+  size_t total = 0, inuse = 0;
 
   /* registries */
   while (pic->regs != NULL) {
@@ -765,10 +770,16 @@ gc_sweep_phase(pic_state *pic)
 
   gc_sweep_symbols(pic);
 
+  page = pic->heap->pages;
   while (page) {
-    gc_sweep_page(pic, page);
+    inuse += gc_sweep_page(pic, page);
+    total += page->endp - page->basep;
     page = page->next;
   }
+
+  if (PIC_PAGE_REQUEST_THRESHOLD(total) <= inuse) {
+    heap_morecore(pic);
+  }
 }
 
 void
diff --git a/extlib/benz/include/picrin/config.h b/extlib/benz/include/picrin/config.h
index 5c284de1..4645ffcc 100644
--- a/extlib/benz/include/picrin/config.h
+++ b/extlib/benz/include/picrin/config.h
@@ -33,6 +33,8 @@
 
 /* #define PIC_HEAP_PAGE_SIZE 10000 */
 
+/* #define PIC_PAGE_REQUEST_THRESHOLD(total) ((total) * 77 / 100) */
+
 /* #define PIC_STACK_SIZE 1024 */
 
 /* #define PIC_RESCUE_SIZE 30 */
@@ -127,6 +129,10 @@
 # define PIC_HEAP_PAGE_SIZE (2 * 1024 * 1024)
 #endif
 
+#ifndef PIC_PAGE_REQUEST_THRESHOLD
+# define PIC_PAGE_REQUEST_THRESHOLD(total) ((total) * 77 / 100)
+#endif
+
 #ifndef PIC_STACK_SIZE
 # define PIC_STACK_SIZE 2048
 #endif