--- old/src/share/vm/oops/valueKlass.cpp	2016-11-16 09:06:11.638498566 +0100
+++ new/src/share/vm/oops/valueKlass.cpp	2016-11-16 09:06:11.574498564 +0100
@@ -42,13 +42,18 @@
 }
 
 int ValueKlass::first_field_offset() {
-  // Really inefficient, should be cached somewhere
+#ifdef ASSERT
   instanceKlassHandle k(this);
   int first_offset = INT_MAX;
   for (JavaFieldStream fs(k()); !fs.done(); fs.next()) {
     if (fs.offset() < first_offset) first_offset= fs.offset();
   }
-  return first_offset;
+#endif
+  int base_offset = instanceOopDesc::base_offset_in_bytes();
+  // The first field of value types is aligned on a long boundary
+  base_offset = align_size_up(base_offset, BytesPerLong);
+  assert(base_offset = first_offset, "inconsistent offsets");
+  return base_offset;
 }
 
 bool ValueKlass::is_atomic() {