diff -r 9d17f29fe16a -r 23a804fa1d3e src/Structures.cpp
--- a/src/Structures.cpp	Sun Sep 16 22:49:54 2012 -0700
+++ b/src/Structures.cpp	Sun Sep 16 23:15:13 2012 -0700
@@ -20,6 +20,7 @@
 #include "Structures.h"
 #include "Zone.h"
 #include "Types.h"
+#include "Array.h"
 #include "Spaces-inl.h"
 #include "Heap-inl.h"
 
@@ -98,16 +99,23 @@
     // struct allocation, rather than inlined in bytecode, for simplicity.
     if (map->composed()) {
         Local<Descriptor> desc(zone);
-        Local<Struct> child(zone);
-        Local<StructMap> childMap(zone);
+        Local<Object> child(zone);
+        Local<StructMap> childStructMap(zone);
+        Local<ArrayMap> childArrayMap(zone);
+
         for (unsigned i = 0; i < map->composed()->length(); i++) {
             desc = Descriptor::cast(map->composed()->at(i));
 
-            // We don't support composing arrays yet.
-            assert(desc->type()->isStruct());
-
-            childMap = StructMap::cast(desc->type()->newMap());
-            child = Struct::New(zone, childMap, tenure);
+            if (desc->type()->isStruct()) {
+                childStructMap = StructMap::cast(desc->type()->newMap());
+                child = Struct::New(zone, childStructMap, tenure);
+            } else if (desc->type()->isArray()) {
+                childArrayMap = ArrayMap::cast(desc->type()->newMap());
+                if (desc->type()->isFixedLength())
+                    child = Array::NewFixed(zone, childArrayMap, tenure);
+                else
+                    child = Array::NewEmpty(zone, childArrayMap, tenure);
+            }
             if (!child)
                 return NULL;