--- old/src/share/vm/gc_implementation/g1/concurrentMark.cpp	2013-01-08 14:04:35.697911635 -0800
+++ new/src/share/vm/gc_implementation/g1/concurrentMark.cpp	2013-01-08 14:04:35.482019238 -0800
@@ -3242,7 +3242,9 @@
 }
 
 void ConcurrentMark::print_worker_threads_on(outputStream* st) const {
-  _parallel_workers->print_worker_threads_on(st);
+  if (parallel_marking_threads() > 0) {
+    _parallel_workers->print_worker_threads_on(st);
+  }
 }
 
 // We take a break if someone is trying to stop the world.
--- old/src/share/vm/gc_implementation/g1/concurrentMark.hpp	2013-01-08 14:04:36.863813778 -0800
+++ new/src/share/vm/gc_implementation/g1/concurrentMark.hpp	2013-01-08 14:04:36.653365105 -0800
@@ -499,12 +499,12 @@
   }
 
   // accessor methods
-  uint parallel_marking_threads() { return _parallel_marking_threads; }
-  uint max_parallel_marking_threads() { return _max_parallel_marking_threads;}
-  double sleep_factor()             { return _sleep_factor; }
-  double marking_task_overhead()    { return _marking_task_overhead;}
-  double cleanup_sleep_factor()     { return _cleanup_sleep_factor; }
-  double cleanup_task_overhead()    { return _cleanup_task_overhead;}
+  uint parallel_marking_threads() const   { return _parallel_marking_threads; }
+  uint max_parallel_marking_threads()     { return _max_parallel_marking_threads;}
+  double sleep_factor()                   { return _sleep_factor; }
+  double marking_task_overhead()          { return _marking_task_overhead;}
+  double cleanup_sleep_factor()           { return _cleanup_sleep_factor; }
+  double cleanup_task_overhead()          { return _cleanup_task_overhead;}
 
   HeapWord*               finger()        { return _finger;   }
   bool                    concurrent()    { return _concurrent; }