--- old/src/share/vm/gc_implementation/g1/g1RootProcessor.cpp	2015-05-13 14:02:14.362499987 +0200
+++ new/src/share/vm/gc_implementation/g1/g1RootProcessor.cpp	2015-05-13 14:02:14.254496395 +0200
@@ -253,7 +253,7 @@
 
   {
     G1GCParPhaseTimesTracker x(phase_times, G1GCPhaseTimes::ThreadRoots, worker_i);
-    bool is_par = _g1h->n_par_threads() > 0;
+    bool is_par = _g1h->n_par_threads() > 1;
     Threads::possibly_parallel_oops_do(is_par, strong_roots, thread_stack_clds, strong_code);
   }
 }