--- old/src/hotspot/share/gc/z/zBarrier.cpp	2019-12-09 11:24:58.559820324 +0100
+++ new/src/hotspot/share/gc/z/zBarrier.cpp	2019-12-09 11:24:57.324779623 +0100
@@ -84,6 +84,17 @@
     ZHeap::heap()->mark_object<follow, finalizable, publish>(good_addr);
   }
 
+  if (finalizable) {
+    // Make the oop finalizable marked/good, instead of normal marked/good.
+    // This is needed because an object might first becomes finalizable
+    // marked by the GC, and then loaded by a mutator thread. In this case,
+    // the mutator thread must be able to tell that the object needs to be
+    // strongly marked. The finalizable bit in the oop exists to make sure
+    // that a load of a finalizable marked oop will fall into the barrier
+    // slow path so that we can mark the object as strongly reachable.
+    return ZAddress::finalizable_good(good_addr);
+  }
+
   return good_addr;
 }
 
@@ -166,25 +177,17 @@
 // Mark barrier
 //
 uintptr_t ZBarrier::mark_barrier_on_oop_slow_path(uintptr_t addr) {
+  assert(during_mark(), "Invalid phase");
+
+  // Mark
   return mark<Follow, Strong, Overflow>(addr);
 }
 
 uintptr_t ZBarrier::mark_barrier_on_finalizable_oop_slow_path(uintptr_t addr) {
-  const uintptr_t good_addr = mark<Follow, Finalizable, Overflow>(addr);
-  if (ZAddress::is_good(addr)) {
-    // If the oop was already strongly marked/good, then we do
-    // not want to downgrade it to finalizable marked/good.
-    return good_addr;
-  }
+  assert(during_mark(), "Invalid phase");
 
-  // Make the oop finalizable marked/good, instead of normal marked/good.
-  // This is needed because an object might first becomes finalizable
-  // marked by the GC, and then loaded by a mutator thread. In this case,
-  // the mutator thread must be able to tell that the object needs to be
-  // strongly marked. The finalizable bit in the oop exists to make sure
-  // that a load of a finalizable marked oop will fall into the barrier
-  // slow path so that we can mark the object as strongly reachable.
-  return ZAddress::finalizable_good(good_addr);
+  // Mark
+  return mark<Follow, Finalizable, Overflow>(addr);
 }
 
 uintptr_t ZBarrier::mark_barrier_on_root_oop_slow_path(uintptr_t addr) {