diff --git a/limmutable.c b/limmutable.c
index 2617701..2a547ca 100644
--- a/limmutable.c
+++ b/limmutable.c
@@ -19,7 +19,6 @@
 *         hash buckets: weak-keyed map from instance userdata -> table of values
 *     __buckets: weak-keyed map from instance userdata -> hash bucket (used to manage hash bucket lifetimes)
 *     __fields: list of named fields
-*     __indices: map from field names to the index in the instance table where the value is stored
 *     metamethods, methods, class variables, etc.
 */
 
@@ -50,11 +49,11 @@ static int WEAK_VALUE_METATABLE;
 // constructed classes to have the same metatable:
 //  {__new=Lcreate_instance, __tostring=function(cls) return cls.name or 'immutable(...)' end}
 static int SHARED_CLASS_METATABLE;
-static int SUPER_METHODS;
+static int SUPER_METHODS, NIL_SENTINEL;
 
 typedef struct {
     int hash;
-    size_t len;
+    size_t array_len;
 } immutable_info_t;
 
 #define IMMUTABLE_GETVALUE(i) if (from_table) {\
@@ -68,8 +67,12 @@ typedef struct {
     if (i <= num_args) {\
         lua_pushvalue(L, 1+i);\
     } else {\
-        lua_pushnil(L);\
+        lua_pushlightuserdata(L, &NIL_SENTINEL);\
     }\
+}\
+if (lua_isnil(L, -1)) {\
+    lua_pop(L, 1);\
+    lua_pushlightuserdata(L, &NIL_SENTINEL);\
 }
 
 static inline int _create_instance(lua_State *L, int from_table)
@@ -79,6 +82,7 @@ static inline int _create_instance(lua_State *L, int from_table)
     int fields_index = lua_gettop(L);
     size_t num_fields = lua_objlen(L, -1);
     size_t num_values = from_table ? (num_fields + lua_objlen(L, 2)) : (num_args >= num_fields ? num_args : num_fields);
+    size_t array_len = num_values - num_fields;
     
     // Compute the hash and populate the values table:
     // Stack: [fields]
@@ -107,11 +111,15 @@ static inline int _create_instance(lua_State *L, int from_table)
                 // Arbitrarily chosen values
                 item_hash = lua_toboolean(L, -1)? 0x82684f71 : 0x88d66f2a;
                 break;
+            case LUA_TLIGHTUSERDATA:
+                if (lua_touserdata(L, -1) == &NIL_SENTINEL) {
+                    item_hash = (1000003 * type) ^ (lua_Integer)lua_topointer(L, -1);
+                    break;
+                }
             case LUA_TTABLE:
             case LUA_TFUNCTION:
             case LUA_TUSERDATA:
             case LUA_TTHREAD:
-            case LUA_TLIGHTUSERDATA:
                 item_hash = (1000003 * type) ^ (lua_Integer)lua_topointer(L, -1);
                 break;
             case LUA_TSTRING:
@@ -163,12 +171,14 @@ static inline int _create_instance(lua_State *L, int from_table)
             // Stack: [fields, __instances, bucket, hash_collider_inst, collider_table]
             // Shallow equality check:
             immutable_info_t *collider_info = (immutable_info_t*)lua_touserdata(L, -2);
-            if (collider_info->len != num_values) {
+            if (collider_info->array_len != array_len) {
                 lua_pop(L, 1);
                 goto next_bucket_item;
             }
-            for (size_t i = 1; i <= num_values; i++) {
-                lua_rawgeti(L, -1, i);
+            // Stack: [fields, __instances, bucket, hash_collider_inst, collider_table]
+            for (size_t i = 1; i <= num_fields; i++) {
+                lua_rawgeti(L, fields_index, i);
+                lua_gettable(L, -2);
                 IMMUTABLE_GETVALUE(i);
                 // Stack: [fields, __instances, bucket, hash_collider_inst, collider_table, collider_val, inst_val]
                 if (! lua_rawequal(L, -1, -2)) { // If the i'th entry doesn't match the i'th arg
@@ -178,6 +188,17 @@ static inline int _create_instance(lua_State *L, int from_table)
                     lua_pop(L, 2);
                 }
             }
+            for (size_t i = 1; i <= array_len; i++) {
+                lua_rawgeti(L, -1, i);
+                IMMUTABLE_GETVALUE(i+num_fields);
+                // Stack: [fields, __instances, bucket, hash_collider_inst, collider_table, collider_val, inst_val]
+                if (! lua_rawequal(L, -1, -2)) { // If the i'th entry doesn't match the i'th arg
+                    lua_pop(L, 3);
+                    goto next_bucket_item;
+                } else {
+                    lua_pop(L, 2);
+                }
+            }
             // bucket item matches
             // Stack: [fields, __instances, bucket, hash_collider_inst, collider_table]
             lua_pop(L, 1);
@@ -194,7 +215,7 @@ static inline int _create_instance(lua_State *L, int from_table)
     // Stack: [fields, __instances, bucket, inst_userdata]
     int userdata_index = lua_gettop(L);
     userdata->hash = hash;
-    userdata->len = num_values;
+    userdata->array_len = array_len;
     
     lua_pushvalue(L, 1);
     // Stack: [fields, __instances, bucket, inst_userdata, cls]
@@ -214,9 +235,14 @@ static inline int _create_instance(lua_State *L, int from_table)
     
     lua_pushvalue(L, userdata_index);
     // Stack: [fields, __instances, bucket, inst_userdata, inst_userdata]
-    lua_createtable(L, num_values, 0);
-    for (size_t i=1; i <= num_values; i++) {
+    lua_createtable(L, num_values-num_fields, num_fields);
+    for (size_t i=1; i <= num_fields; i++) {
+        lua_rawgeti(L, fields_index, i);
         IMMUTABLE_GETVALUE(i);
+        lua_settable(L, -3);
+    }
+    for (size_t i=1; i <= array_len; i++) {
+        IMMUTABLE_GETVALUE(i+num_fields);
         lua_rawseti(L, -2, i);
     }
     // Stack: [fields, __instances, bucket, inst_userdata, inst_userdata, inst_table]
@@ -263,49 +289,24 @@ static int Llen(lua_State *L)
         luaL_error(L, "invalid type");
     }
     immutable_info_t *info = (immutable_info_t *)lua_touserdata(L, 1);
-    lua_getfield(L, -1, "__fields");
-    size_t len = info->len - lua_objlen(L, -1);
-    lua_pushinteger(L, len);
+    lua_pushinteger(L, info->array_len);
     return 1;
 }
 
-static int Linst_index(lua_State *L)
+static int Lindex(lua_State *L)
 {
     // Return inst[key], <whether inst has key>
     luaL_checktype(L, 1, LUA_TUSERDATA);
     if (! lua_getmetatable(L, 1)) {
         luaL_error(L, "invalid type");
     }
+    int class_index = lua_gettop(L);
     // Stack: [mt]
     immutable_info_t *info = (immutable_info_t*)lua_touserdata(L, 1);
     if (! info) {
         luaL_error(L, "invalid type");
     }
 
-    lua_getfield(L, -1, "__fields");
-    size_t num_fields = lua_objlen(L, -1);
-    lua_pop(L, 1);
-
-    // Stack: [mt]
-    lua_getfield(L, -1, "__indices");
-    // Stack: [mt, indices]
-    lua_pushvalue(L, 2);
-    lua_gettable(L, -2);
-    // Stack: [mt, indices, index]
-    int index;
-    if (lua_isnil(L, -1)) {
-        if (! lua_isinteger(L, 2)) {
-            return 0;
-        }
-        index = lua_tointeger(L, 2) + num_fields;
-    } else {
-        index = lua_tointeger(L, -1);
-    }
-    lua_pop(L, 2);
-    // Stack: [mt]
-    if (! (0 < index && index <= (int)info->len)) {
-        return 0;
-    }
     // Stack: [mt]
     lua_getfield(L, -1, "__instances");
     // Stack: [mt, buckets]
@@ -321,28 +322,20 @@ static int Linst_index(lua_State *L)
     if (lua_isnil(L, -1)) {
         luaL_error(L, "Failed to find instance");
     }
-    lua_rawgeti(L, -1, index);
-    lua_pushboolean(L, 1);
-    return 2;
-}
-
-static int Lindex(lua_State *L)
-{
-    int ret = Linst_index(L);
-    if (ret > 0) {
-        return ret;
-    }
-    // Fall back to class:
-    lua_getmetatable(L, 1);
-    // Stack: [..., mt]
     lua_pushvalue(L, 2);
-    // Stack: [..., mt, key]
     lua_gettable(L, -2);
-    // Stack: [..., mt, value]
-    if (! lua_isnil(L, -1)) {
+    if (lua_isnil(L, -1)) {
+        // Fall back to class:
+        lua_pushvalue(L, 2);
+        lua_gettable(L, class_index);
         return 1;
     }
-    return 0;
+    if (lua_islightuserdata(L, -1) && lua_touserdata(L, -1) == &NIL_SENTINEL) {
+        lua_pop(L, 1);
+        lua_pushnil(L);
+    }
+    lua_pushboolean(L, 1);
+    return 2;
 }
 
 static int Ltostring(lua_State *L)
@@ -382,10 +375,13 @@ static int Ltostring(lua_State *L)
     }
     int inst_table_index = lua_gettop(L);
     // Stack: [mt, buckets, bucket, inst_table]
+    lua_getfield(L, cls_index, "__fields");
+    int fields_index = lua_gettop(L);
     lua_getglobal(L, "tostring");
     int tostring_index = lua_gettop(L);
-    // Stack: [mt, buckets, bucket, inst_table, tostring]
-    int n = info->len, i = 1;
+    // Stack: [mt, buckets, bucket, inst_table, __fields, tostring]
+    int num_fields = lua_objlen(L, fields_index);
+    int n = num_fields + info->array_len, i = 1;
     if (i <= n) {
         goto first_list_item;
     }
@@ -395,7 +391,16 @@ static int Ltostring(lua_State *L)
       first_list_item:
         lua_pushvalue(L, tostring_index);
         // Stack: [mt, buckets, bucket, inst_table, tostring, ???, tostring]
-        lua_rawgeti(L, inst_table_index, i);
+        if (i <= num_fields) {
+            lua_rawgeti(L, fields_index, i);
+            lua_gettable(L, inst_table_index);
+        } else {
+            lua_rawgeti(L, inst_table_index, i - num_fields);
+        }
+        if (lua_islightuserdata(L, -1) && lua_touserdata(L, -1) == &NIL_SENTINEL) {
+            lua_pop(L, 1);
+            lua_pushnil(L);
+        }
         // Stack: [mt, buckets, bucket, inst_table, tostring, ???, tostring, value]
         int quotes = lua_type(L, -1) == LUA_TSTRING;
         lua_call(L, 1, 1);
@@ -420,7 +425,6 @@ static int Lnexti(lua_State *L)
     if (! lua_getmetatable(L, 1)) {
         luaL_error(L, "invalid type");
     }
-    int cls_index = lua_gettop(L);
     // Stack: [mt]
     lua_getfield(L, -1, "__instances");
     // Stack: [mt, buckets]
@@ -428,11 +432,8 @@ static int Lnexti(lua_State *L)
     if (! info) {
         luaL_error(L, "invalid type");
     }
-    int i = lua_isnil(L, 2) ? 1 : lua_tointeger(L, 2)+1;
-    lua_getfield(L, cls_index, "__fields");
-    int num_fields = lua_objlen(L, -1);
-    lua_pop(L, 1);
-    if (i + num_fields > (int)info->len) {
+    int i = lua_tointeger(L, 2)+1;
+    if (i > (int)info->array_len) {
         return 0;
     }
     lua_rawgeti(L, -1, info->hash);
@@ -446,8 +447,12 @@ static int Lnexti(lua_State *L)
     // Stack: [mt, buckets, bucket, inst_table]
     lua_pushinteger(L, i);
     // Stack: [mt, buckets, bucket, inst_table, i]
-    lua_rawgeti(L, -2, i + num_fields);
+    lua_rawgeti(L, -2, i);
     // Stack: [mt, buckets, bucket, inst_table, i, table[i]]
+    if (lua_islightuserdata(L, -1) && lua_touserdata(L, -1) == &NIL_SENTINEL) {
+        lua_pop(L, 1);
+        lua_pushnil(L);
+    }
     return 2;
 }
 
@@ -457,8 +462,8 @@ static int Lipairs(lua_State *L)
     // Stack: [Lnexti]
     lua_pushvalue(L, 1);
     // Stack: [Lnexti, inst_udata]
-    lua_pushnil(L);
-    // Stack: [Lnexti, inst_udata, nil]
+    lua_pushinteger(L, 0);
+    // Stack: [Lnexti, inst_udata, 0]
     return 3;
 }
 
@@ -467,57 +472,31 @@ static int Lnext(lua_State *L)
     if (! lua_getmetatable(L, 1)) {
         luaL_error(L, "invalid type");
     }
-    int cls_index = lua_gettop(L);
     // Stack: [mt]
-    lua_getfield(L, cls_index, "__fields");
-    int fields_index = lua_gettop(L);
-    lua_getfield(L, cls_index, "__indices");
-    int indices_index = lua_gettop(L);
-    lua_getfield(L, cls_index, "__instances");
-    // Stack: [..., buckets]
+    lua_getfield(L, -1, "__instances");
+    // Stack: [mt, buckets]
     immutable_info_t *info = (immutable_info_t*)lua_touserdata(L, 1);
     if (! info) {
         luaL_error(L, "invalid type");
     }
     lua_rawgeti(L, -1, info->hash);
-    // Stack: [..., buckets, bucket]
+    // Stack: [mt, buckets, bucket]
     if (lua_isnil(L, -1)) {
         luaL_error(L, "Failed to find hash bucket");
     }
     lua_pushvalue(L, 1);
-    // Stack: [..., buckets, bucket, inst_udata]
+    // Stack: [mt, buckets, bucket, inst_udata]
     lua_rawget(L, -2);
-    // Stack: [..., buckets, bucket, inst_table]
-    size_t num_fields = lua_objlen(L, fields_index);
-    int index;
-    if (lua_isnil(L, 2)) {
-        index = 1;
-    } else {
-        lua_pushvalue(L, 2);
-        // Stack: [..., buckets, bucket, inst_table, k]
-        lua_gettable(L, indices_index);
-        // Stack: [..., buckets, bucket, inst_table, i]
-        if (! lua_isnil(L, -1)) {
-            index = lua_tointeger(L, -1) + 1;
-        } else {
-            index = lua_tointeger(L, 2) + num_fields + 1;
-        }
-        lua_pop(L, 1);
-    }
-    // Stack: [..., buckets, bucket, inst_table]
-    if (! (0 < index && index <= (int)info->len)) {
+    // Stack: [mt, buckets, bucket, inst_table]
+    lua_pushvalue(L, 2);
+    // TODO: this is in a random order, and it might be good to force it to be in the same order as __fields
+    if (lua_next(L, -2) == 0) {
         return 0;
     }
-
-    // Now find field name
-    if (index <= (int)num_fields) {
-        lua_rawgeti(L, fields_index, index);
-    } else {
-        lua_pushinteger(L, index - num_fields);
+    if (lua_islightuserdata(L, -1) && lua_touserdata(L, -1) == &NIL_SENTINEL) {
+        lua_pop(L, 1);
+        lua_pushnil(L);
     }
-    // Stack: [..., buckets, bucket, inst_table, k2]
-    lua_rawgeti(L, -2, index);
-    // Stack: [..., buckets, bucket, inst_table, k2, value2]
     return 2;
 }
 
@@ -605,39 +584,18 @@ static int Lmake_class(lua_State *L)
 
     // Stack: [CLS]
     switch (num_args == 0 ? LUA_TNIL : lua_type(L, 1)) {
-        case LUA_TTABLE: {
-            // CLS.__fields = arg1
+        case LUA_TTABLE:
             lua_pushvalue(L, 1);
-            // Stack: [CLS, __fields]
-            lua_setfield(L, -2, "__fields");
-            // Stack: [CLS]
-
-            size_t n = lua_objlen(L, 1);
-            lua_createtable(L, 0, n);
-            // Stack: [CLS, __indices]
-            lua_pushnil(L);
-            while (lua_next(L, 1) != 0) {
-                // Stack: [CLS, __indices, i, fieldname]
-                lua_pushvalue(L, -2);
-                // Stack: [CLS, __indices, i, fieldname, i]
-                lua_settable(L, -4);
-                // Stack: [CLS, __indices, i]
-            }
-            lua_setfield(L, -2, "__indices");
             break;
-        }
-        case LUA_TNIL: case LUA_TNONE: {
-            // If no fields were passed in, set __fields and __indices to empty tables
+        case LUA_TNIL: case LUA_TNONE:
+            // If no fields were passed in, set __fields to empty table
             lua_createtable(L, 0, 0);
-            lua_setfield(L, -2, "__fields");
-            lua_createtable(L, 0, 0);
-            lua_setfield(L, -2, "__indices");
             break;
-        }
         default: {
             luaL_error(L, "immutable expected the fields to be either table or nil");
         }
     }
+    lua_setfield(L, -2, "__fields");
     // Stack: [CLS]
     lua_pushlightuserdata(L, (void*)&SHARED_CLASS_METATABLE);
     lua_gettable(L, LUA_REGISTRYINDEX);