diff --git a/src/gc.c b/src/gc.c
index c8f25d46..eda14f25 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -164,7 +164,6 @@ gc_mark_phase(pic_state *pic)
   for (stack = pic->stbase; stack != pic->sp; ++stack) {
     gc_mark(pic, *stack);
   }
-  gc_mark(pic, *stack);
 
   /* arena */
   for (i = 0; i < pic->arena_idx; ++i) {