diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index d340e4b..0a97128 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -540,7 +540,8 @@
               map()->NextFreePropertyIndex()));
   }
   ASSERT(map()->has_fast_elements() ==
-         (elements()->map() == Heap::fixed_array_map()));
+         (elements()->map() == Heap::fixed_array_map() ||
+          elements()->map() == Heap::fixed_cow_array_map()));
   ASSERT(map()->has_fast_elements() == HasFastElements());
 }