--- old/src/share/vm/memory/genCollectedHeap.cpp	2015-04-01 13:16:30.315821698 +0200
+++ new/src/share/vm/memory/genCollectedHeap.cpp	2015-04-01 13:16:30.199821703 +0200
@@ -561,7 +561,8 @@
 }
 
 void GenCollectedHeap::set_par_threads(uint t) {
-  SharedHeap::set_par_threads(t);
+  assert(t == 0 || !UseSerialGC, "Cannot have parallel threads");
+  CollectedHeap::set_par_threads(t);
   set_n_termination(t);
 }