--- old/src/hotspot/share/gc/shared/gcConfiguration.cpp	2018-06-01 22:29:50.856733338 +0200
+++ new/src/hotspot/share/gc/shared/gcConfiguration.cpp	2018-06-01 22:29:50.600722287 +0200
@@ -43,6 +43,10 @@
     return ParNew;
   }
 
+  if (UseZGC) {
+    return NA;
+  }
+
   return DefNew;
 }
 
@@ -59,6 +63,10 @@
     return ParallelOld;
   }
 
+  if (UseZGC) {
+    return Z;
+  }
+
   return SerialOld;
 }