--- old/src/hotspot/share/gc/z/zArguments.cpp	2018-06-26 16:44:22.740351938 -0400
+++ new/src/hotspot/share/gc/z/zArguments.cpp	2018-06-26 16:44:22.524351946 -0400
@@ -82,6 +82,11 @@
   // CompressedOops/UseCompressedClassPointers not supported
   FLAG_SET_DEFAULT(UseCompressedOops, false);
   FLAG_SET_DEFAULT(UseCompressedClassPointers, false);
+  FLAG_SET_DEFAULT(UseSharedSpaces, false);  // requires CompressedOops and CompressedClassPointers
+
+  if (DumpSharedSpaces) {
+    vm_exit_during_initialization("DumpSharedSpaces (-Xshare:dump) is not supported with ZGC.");
+  }
 
   // ClassUnloading not (yet) supported
   FLAG_SET_DEFAULT(ClassUnloading, false);