diff -r 04f4e983c2f7 -r 767cdb97f103 src/hotspot/share/gc/shared/gcConfiguration.cpp
--- a/src/hotspot/share/gc/shared/gcConfiguration.cpp	Tue Jun 12 07:52:30 2018 -0700
+++ b/src/hotspot/share/gc/shared/gcConfiguration.cpp	Tue Jun 12 17:40:28 2018 +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;
 }