--- old/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	2019-11-21 11:53:41.851458731 +0100
+++ new/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp	2019-11-21 11:53:41.591454332 +0100
@@ -629,7 +629,7 @@
 
 void ShenandoahHeap::decrease_used(size_t bytes) {
   assert(used() >= bytes, "never decrease heap size by more than we've left");
-  Atomic::sub(bytes, &_used);
+  Atomic::sub(&_used, bytes);
 }
 
 void ShenandoahHeap::increase_allocated(size_t bytes) {