--- old/src/hotspot/share/gc/parallel/parallelArguments.cpp	2019-12-18 16:36:50.149529557 +0100
+++ new/src/hotspot/share/gc/parallel/parallelArguments.cpp	2019-12-18 16:36:49.977527233 +0100
@@ -45,7 +45,6 @@
 void ParallelArguments::initialize() {
   GCArguments::initialize();
   assert(UseParallelGC, "Error");
-  FLAG_SET_DEFAULT(UseParallelGC, true);
 
   // If no heap maximum was requested explicitly, use some reasonable fraction
   // of the physical memory, up to a maximum of 1GB.