--- old/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	2012-12-21 12:59:44.000000000 +0100
+++ new/src/share/vm/gc_implementation/parNew/parNewGeneration.cpp	2012-12-21 12:59:44.000000000 +0100
@@ -1625,5 +1625,5 @@
 }
 
 bool ParNewGeneration::in_use() {
-  return UseParNewGC && ParallelGCThreads > 0;
+  return UseParNewGC;
 }
--- old/src/share/vm/memory/collectorPolicy.cpp	2012-12-21 12:59:44.000000000 +0100
+++ new/src/share/vm/memory/collectorPolicy.cpp	2012-12-21 12:59:44.000000000 +0100
@@ -818,7 +818,7 @@
   if (_generations == NULL)
     vm_exit_during_initialization("Unable to allocate gen spec");
 
-  if (UseParNewGC && ParallelGCThreads > 0) {
+  if (UseParNewGC) {
     _generations[0] = new GenerationSpec(Generation::ParNew, _initial_gen0_size, _max_gen0_size);
   } else {
     _generations[0] = new GenerationSpec(Generation::DefNew, _initial_gen0_size, _max_gen0_size);
@@ -831,10 +831,9 @@
 
 void MarkSweepPolicy::initialize_gc_policy_counters() {
   // initialize the policy counters - 2 collectors, 3 generations
-  if (UseParNewGC && ParallelGCThreads > 0) {
+  if (UseParNewGC) {
     _gc_policy_counters = new GCPolicyCounters("ParNew:MSC", 2, 3);
-  }
-  else {
+  } else {
     _gc_policy_counters = new GCPolicyCounters("Copy:MSC", 2, 3);
   }
 }
--- old/src/share/vm/memory/tenuredGeneration.cpp	2012-12-21 12:59:45.000000000 +0100
+++ new/src/share/vm/memory/tenuredGeneration.cpp	2012-12-21 12:59:45.000000000 +0100
@@ -62,7 +62,7 @@
                                        _virtual_space.reserved_size(),
                                        _the_space, _gen_counters);
 #ifndef SERIALGC
-  if (UseParNewGC && ParallelGCThreads > 0) {
+  if (UseParNewGC) {
     typedef ParGCAllocBufferWithBOT* ParGCAllocBufferWithBOTPtr;
     _alloc_buffers = NEW_C_HEAP_ARRAY(ParGCAllocBufferWithBOTPtr,
                                       ParallelGCThreads, mtGC);
--- old/src/share/vm/runtime/arguments.cpp	2012-12-21 12:59:46.000000000 +0100
+++ new/src/share/vm/runtime/arguments.cpp	2012-12-21 12:59:45.000000000 +0100
@@ -1083,10 +1083,6 @@
   }
 }
 
-// If the user has chosen ParallelGCThreads > 0, we set UseParNewGC
-// if it's not explictly set or unset. If the user has chosen
-// UseParNewGC and not explicitly set ParallelGCThreads we
-// set it, unless this is a single cpu machine.
 void Arguments::set_parnew_gc_flags() {
   assert(!UseSerialGC && !UseParallelOldGC && !UseParallelGC && !UseG1GC,
          "control point invariant");
@@ -1095,14 +1091,14 @@
   // Turn off AdaptiveSizePolicy for parnew until it is complete.
   disable_adaptive_size_policy("UseParNewGC");
 
-  if (ParallelGCThreads == 0) {
-    FLAG_SET_DEFAULT(ParallelGCThreads,
-                     Abstract_VM_Version::parallel_worker_threads());
-    if (ParallelGCThreads == 1) {
-      FLAG_SET_DEFAULT(UseParNewGC, false);
-      FLAG_SET_DEFAULT(ParallelGCThreads, 0);
+  if (FLAG_IS_DEFAULT(ParallelGCThreads)) {
+    assert(ParallelGCThreads == 0, "Default value for ParallelGCThreads should be 0");
+    uint par_gc_threads = Abstract_VM_Version::parallel_worker_threads();
+    if (par_gc_threads > 1) {
+      FLAG_SET_DEFAULT(ParallelGCThreads, par_gc_threads);
     }
   }
+
   if (UseParNewGC) {
     // By default YoungPLABSize and OldPLABSize are set to 4096 and 1024 respectively,
     // these settings are default for Parallel Scavenger. For ParNew+Tenured configuration