--- old/src/hotspot/share/prims/jvmtiEnv.cpp	2018-10-11 11:58:42.851075413 +0200
+++ new/src/hotspot/share/prims/jvmtiEnv.cpp	2018-10-11 11:58:42.698076781 +0200
@@ -470,7 +470,8 @@
 JvmtiEnv::GetObjectSize(jobject object, jlong* size_ptr) {
   oop mirror = JNIHandles::resolve_external_guard(object);
   NULL_CHECK(mirror, JVMTI_ERROR_INVALID_OBJECT);
-  *size_ptr = (jlong)Universe::heap()->obj_size(mirror) * wordSize;
+  size_t obj_size = mirror->size();
+  *size_ptr = (jlong)Universe::heap()->cell_size(obj_size) * wordSize;
   return JVMTI_ERROR_NONE;
 } /* end GetObjectSize */