diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index b60e54d..0b5ff99 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -539,6 +539,9 @@
              (map()->inobject_properties() + properties()->length() -
               map()->NextFreePropertyIndex()));
   }
+  ASSERT(map()->has_fast_elements() ==
+         (elements()->map() == Heap::fixed_array_map()));
+  ASSERT(map()->has_fast_elements() == HasFastElements());
 }