diff -r e92153ed8bdc -r 29b0d0b61615 src/hotspot/share/gc/g1/g1FullGCAdjustTask.cpp
--- a/src/hotspot/share/gc/g1/g1FullGCAdjustTask.cpp	Mon Nov 25 12:30:24 2019 +0100
+++ b/src/hotspot/share/gc/g1/g1FullGCAdjustTask.cpp	Mon Nov 25 12:31:39 2019 +0100
@@ -101,7 +101,7 @@
 
   // Adjust the weak roots.
 
-  if (Atomic::add(1u, &_references_done) == 1u) { // First incr claims task.
+  if (Atomic::add(&_references_done, 1u) == 1u) { // First incr claims task.
     G1CollectedHeap::heap()->ref_processor_stw()->weak_oops_do(&_adjust);
   }