diff --git a/gc.c b/gc.c
index 38dcde1a..bdce29ae 100644
--- a/gc.c
+++ b/gc.c
@@ -932,6 +932,9 @@ void gc_collector_trace()
       while (m->last_read < m->last_write) {
         clean = 0;
         (m->last_read)++;
+printf("gc_mark_black mark buffer %p, last_read = %d last_write = %d\n", 
+(m->mark_buffer)[m->last_read],
+m->last_read, m->last_write);
         gc_mark_black((m->mark_buffer)[m->last_read]);
         gc_empty_collector_stack();
       }
@@ -1006,6 +1009,9 @@ void gc_mark_black(object obj)
       mark(obj) = markColor;
       printf("marked %p %d\n", obj, markColor);
     }
+    else {
+      printf("not marking stack obj %p %d\n", obj, markColor);
+    }
   }
 }
 
diff --git a/runtime.c b/runtime.c
index 9114ec66..69b9904d 100644
--- a/runtime.c
+++ b/runtime.c
@@ -2441,7 +2441,7 @@ void gc_mark_globals()
   printf("(gc_mark_globals heap: %p size: %d)\n", h, (unsigned int)gc_heap_total_size(h));
 #endif
   // Mark global variables
-printf("Cyc_global_variables %p\n");
+printf("Cyc_global_variables %p\n", Cyc_global_variables);
   gc_mark_black(Cyc_global_variables); // Internal global used by the runtime
                                        // Marking it ensures all glos are marked
   {