diff a/src/hotspot/share/gc/shenandoah/shenandoahMark.inline.hpp b/src/hotspot/share/gc/shenandoah/shenandoahMark.inline.hpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahMark.inline.hpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahMark.inline.hpp
@@ -113,11 +113,11 @@
 template <ShenandoahGenerationType GENERATION>
 inline void ShenandoahMark::count_liveness(ShenandoahLiveData* live_data, oop obj, Klass* klass, uint worker_id) {
   const ShenandoahHeap* const heap = ShenandoahHeap::heap();
   const size_t region_idx = heap->heap_region_index_containing(obj);
   ShenandoahHeapRegion* const region = heap->get_region(region_idx);
-  const size_t size = obj->size_given_klass(klass);
+  const size_t size = obj->size_given_mark_and_klass(obj->mark(), klass);
 
   // Age census for objects in the young generation
   if (GENERATION == YOUNG || (GENERATION == GLOBAL && region->is_young())) {
     assert(heap->mode()->is_generational(), "Only if generational");
     assert(region->is_young(), "Only for young objects");