diff --git a/gc.c b/gc.c
index a561dffa..df20726f 100644
--- a/gc.c
+++ b/gc.c
@@ -711,7 +711,7 @@ void gc_empty_collector_stack()
 {
   // Mark stack is only used by the collector thread, so no sync needed
   while (mark_stack_i > 0) { // not empty
-    mark_stack--;
+    mark_stack_i--;
     gc_mark_black(mark_stack[mark_stack_i]);
   }
 }