diff -r e92153ed8bdc -r 29b0d0b61615 src/hotspot/share/gc/z/zMarkStackAllocator.cpp
--- a/src/hotspot/share/gc/z/zMarkStackAllocator.cpp	Mon Nov 25 12:30:24 2019 +0100
+++ b/src/hotspot/share/gc/z/zMarkStackAllocator.cpp	Mon Nov 25 12:31:39 2019 +0100
@@ -110,8 +110,8 @@
 
   // Increment top before end to make sure another
   // thread can't steal out newly expanded space.
-  addr = Atomic::add(size, &_top) - size;
-  Atomic::add(expand_size, &_end);
+  addr = Atomic::add(&_top, size) - size;
+  Atomic::add(&_end, expand_size);
 
   return addr;
 }