diff --git a/limmutable.c b/limmutable.c
index 5e519d3..f6caeaa 100644
--- a/limmutable.c
+++ b/limmutable.c
@@ -21,6 +21,10 @@
 #define lua_objlen(L, i) lua_rawlen(L, i)
 #define luaL_register(L, _, R) luaL_setfuncs(L, R, 0)
 #endif
+// Lua 5.3 introduced lua_isinteger, fall back to lua_isnumber
+#if LUA_VERSION_NUM < 503
+#define lua_isinteger(L, i) lua_isnumber(L, i)
+#endif
 
 #if !defined(LUAI_HASHLIMIT)
 #define LUAI_HASHLIMIT		5
@@ -37,21 +41,79 @@ static int WEAK_VALUE_METATABLE;
 //  {__new=Lcreate_instance, __tostring=function(cls) return cls.name or 'immutable(...)' end}
 static int SHARED_CLASS_METATABLE;
 
+typedef struct {
+    unsigned long long hash;
+    size_t len;
+} immutable_info_t;
+
+static int Lhash(lua_State *L)
+{
+    lua_Integer hash = 0x9a937c4d; // Seed
+    lua_Integer n = luaL_checkinteger(L, 1);
+    for (lua_Integer i=2; i <= lua_gettop(L); i++) {
+        lua_Integer item_hash;
+        int type = i > n ? LUA_TNIL : lua_type(L, i);
+        switch (type) {
+            case LUA_TNIL: case LUA_TNONE:
+                // Arbitrarily chosen value
+                item_hash = 0x97167da9;
+                break;
+            case LUA_TNUMBER:
+                {
+                    // Cast float bits to integer
+                    lua_Number num = lua_tonumber(L, i);
+                    item_hash = *((lua_Integer*)&num);
+                    if (item_hash == 0) {
+                        item_hash = 0x2887c992;
+                    }
+                    break;
+                }
+            case LUA_TBOOLEAN:
+                // Arbitrarily chosen values
+                item_hash = lua_toboolean(L, i)? 0x82684f71 : 0x88d66f2a;
+                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, i);
+                break;
+            case LUA_TSTRING:
+                {
+                    // Algorithm taken from Lua 5.3's implementation
+                    size_t len;
+                    const char *str = lua_tolstring(L, i, &len);
+                    item_hash = len ^ 0xd2e9e9ac; // Arbitrary seed
+                    size_t step = (len >> LUAI_HASHLIMIT) + 1;
+                    for (; len >= step; len -= step)
+                        item_hash ^= ((item_hash<<5) + (item_hash>>2) + (unsigned char)(str[len - 1]));
+                    break;
+                }
+            default:
+                item_hash = 0;
+        }
+        hash = (1000003 * hash) ^ item_hash;
+    }
+    lua_pushinteger(L, hash);
+    return 1;
+}
+
 static int Lcreate_instance(lua_State *L)
 {
     size_t n_args = lua_gettop(L)-1;
     // arg 1: class table, ...
     lua_getfield(L, 1, "__fields");
-    size_t n = lua_objlen(L, -1);
+    size_t n = lua_isnil(L, -1) ? n_args : lua_objlen(L, -1);
     if (n_args > n) {
         luaL_error(L, "Too many args: expected %d, but got %d", n, n_args);
     }
     lua_pop(L, 1);
     
     // Compute the hash:
-    lua_Integer hash = (lua_Integer)lua_topointer(L, 1); // Hash depends on the metatable used in creation
+    unsigned long long hash = 0x9a937c4d; // Seed
     for (lua_Integer i=1; i <=(lua_Integer)n; i++) {
-        lua_Integer item_hash;
+        unsigned long long item_hash;
         int type = n > n_args ? LUA_TNIL : lua_type(L, 1+i);
         switch (type) {
             case LUA_TNIL: case LUA_TNONE:
@@ -63,6 +125,9 @@ static int Lcreate_instance(lua_State *L)
                     // Cast float bits to integer
                     lua_Number num = lua_tonumber(L, 1+i);
                     item_hash = *((lua_Integer*)&num);
+                    if (item_hash == 0) {
+                        item_hash = 0x2887c992;
+                    }
                     break;
                 }
             case LUA_TBOOLEAN:
@@ -74,7 +139,7 @@ static int Lcreate_instance(lua_State *L)
             case LUA_TUSERDATA:
             case LUA_TTHREAD:
             case LUA_TLIGHTUSERDATA:
-                item_hash = (lua_Integer)lua_topointer(L, 1+i);
+                item_hash = (1000003 * type) ^ (lua_Integer)lua_topointer(L, i);
                 break;
             case LUA_TSTRING:
                 {
@@ -152,8 +217,9 @@ static int Lcreate_instance(lua_State *L)
 
     // Failed to find an existing instance, so create a new one
     // Stack: [buckets, bucket]
-    lua_Integer* userdata = (lua_Integer*)lua_newuserdata(L, sizeof(lua_Integer));
-    *userdata = hash;
+    immutable_info_t *userdata = (immutable_info_t*)lua_newuserdata(L, sizeof(immutable_info_t));
+    userdata->hash = hash;
+    userdata->len = n;
     
     // Stack [buckets, bucket, inst_userdata]
     lua_pushvalue(L, 1);
@@ -199,29 +265,44 @@ static int Lfrom_table(lua_State *L)
     lua_pushvalue(L, 1);
     // Stack: [mt]
     lua_getfield(L, -1, "__fields");
-    int n = lua_objlen(L, -1);
-    if (! lua_checkstack(L, n)) {
-        luaL_error(L, "Insufficient stack space!");
+    int n;
+    if (lua_isnil(L, -1)) {
+        lua_getfield(L, 2, "n");
+        if (lua_isnil(L, -1)) {
+            luaL_error(L, "table needs an 'n' field to track its length");
+        }
+        n = luaL_checkinteger(L, -1);
+        lua_pop(L, 1);
+        if (! lua_checkstack(L, n)) {
+            luaL_error(L, "Insufficient stack space!");
+        }
+        for (int i = 1; i <= n; i++) {
+            lua_rawgeti(L, 2, i);
+        }
+        // Stack: [mt, table[1], table[2], ... table[table.n]]
+    } else {
+        n = lua_objlen(L, -1);
+        if (! lua_checkstack(L, n)) {
+            luaL_error(L, "Insufficient stack space!");
+        }
+        // Stack: [mt, fields]
+        lua_pushnil(L);
+        while (lua_next(L, -2) != 0) {
+            // Stack: [mt, fields, i, field_i]
+            lua_gettable(L, 2);
+            // Stack: [mt, fields, i, table[field_i]]
+            lua_insert(L, -3);
+            // Stack: [mt, table[field_i], fields, i]
+        }
+        // Stack: [mt, table[field], ..., fields]
+        lua_pop(L, 1);
+        // Stack: [mt, table[field], ...]
     }
-    // Stack: [mt, fields]
-    lua_pushnil(L);
-    int num_args = 0;
-    while (lua_next(L, -2) != 0) {
-        // Stack: [mt, fields, i, field_i]
-        lua_gettable(L, 2);
-        // Stack: [mt, fields, i, table[field_i]]
-        lua_insert(L, -3);
-        // Stack: [mt, table[field_i], fields, i]
-        num_args++;
-    }
-    // Stack: [mt, table[field], ..., fields]
-    lua_pop(L, 1);
-    // Stack: [mt, table[field], ...]
     lua_pushcfunction(L, Lcreate_instance);
     // Stack: [mt, table[field], ..., create]
-    lua_insert(L, -(num_args+2));
+    lua_insert(L, -(n+2));
     // Stack: [create, mt, table[field_1], ...]
-    lua_call(L, num_args+1, 1);
+    lua_call(L, n+1, 1);
     return 1;
 }
 
@@ -238,57 +319,32 @@ static int Lis_instance(lua_State *L)
 
 static int Llen(lua_State *L)
 {
-    if (! lua_getmetatable(L, 1)) {
-        luaL_error(L, "invalid type");
-    }
-    // Stack: [mt]
-    lua_getfield(L, -1, "__fields");
-    // Stack: [mt, fields]
-    lua_pushinteger(L, lua_objlen(L, -1));
+    luaL_checktype(L, 1, LUA_TUSERDATA);
+    immutable_info_t *info = (immutable_info_t *)lua_touserdata(L, 1);
+    lua_pushinteger(L, info->len);
     return 1;
 }
 
 static int Lindex(lua_State *L)
 {
+    luaL_checktype(L, 1, LUA_TUSERDATA);
     if (! lua_getmetatable(L, 1)) {
         luaL_error(L, "invalid type");
     }
+    immutable_info_t *info = (immutable_info_t*)lua_touserdata(L, 1);
+    if (! info) {
+        luaL_error(L, "invalid type");
+    }
+
     // Stack: [mt]
     lua_getfield(L, -1, "__indices");
     // Stack: [mt, indices]
-    lua_pushvalue(L, 2);
-    // Stack: [mt, indices, k]
-    lua_gettable(L, -2);
-    // Stack: [mt, indices, i]
-    if (! lua_isnil(L, -1)) { // Found the field name
-        // Stack: [mt, indices, i]
-        lua_getfield(L, -3, "__instances");
-        // Stack: [mt, indices, i, buckets]
-        lua_Integer* hash_address = (lua_Integer*)lua_touserdata(L, 1);
-        if (! hash_address) {
-            luaL_error(L, "invalid type");
-        }
-        lua_rawgeti(L, -1, *hash_address);
-        // Stack: [mt, indices, i, buckets, bucket]
-        if (lua_isnil(L, -1)) {
-            luaL_error(L, "Failed to find hash bucket for hash: %p", (void*)*hash_address);
-        }
-        lua_pushvalue(L, 1);
-        // Stack: [mt, indices, i, buckets, bucket, inst_udata]
-        lua_rawget(L, -2);
-        // Stack: [mt, indices, i, buckets, bucket, inst_table]
-        lua_rawgeti(L, -1, lua_tointeger(L, -4));
-        return 1;
-    } else if (lua_type(L, 2) == LUA_TNUMBER) {
-        lua_pop(L, 2);
+    if (lua_isnil(L, -1)) {
+        lua_pop(L, 1);
         // Stack: [mt]
         lua_getfield(L, -1, "__instances");
         // Stack: [mt, buckets]
-        lua_Integer* hash_address = (lua_Integer*)lua_touserdata(L, 1);
-        if (! hash_address) {
-            luaL_error(L, "invalid type");
-        }
-        lua_rawgeti(L, -1, *hash_address);
+        lua_rawgeti(L, -1, info->hash);
         // Stack: [mt, buckets, bucket]
         if (lua_isnil(L, -1)) {
             luaL_error(L, "Failed to find hash bucket");
@@ -297,21 +353,43 @@ static int Lindex(lua_State *L)
         // Stack: [mt, buckets, bucket, inst_udata]
         lua_rawget(L, -2);
         // Stack: [mt, buckets, bucket, inst_table]
-        lua_rawgeti(L, -1, lua_tointeger(L, 2));
-        if (! lua_isnil(L, -1)) {
-            // Found numeric index
-            return 1;
-        } else {
-            // Fall back to class
-            // Stack: [mt, buckets, bucket, inst_table, v, k]
+        int i = luaL_checkinteger(L, 2);
+        lua_rawgeti(L, -1, i);
+        return 1;
+    }
+
+    // Stack: [mt, indices]
+    lua_pushvalue(L, 2);
+    // Stack: [mt, indices, k]
+    lua_gettable(L, -2);
+    // Stack: [mt, indices, i]
+    if (lua_isnil(L, -1) && lua_isinteger(L, 2)) {
+        int i = lua_tointeger(L, 2);
+        if (1 <= i && i <= (int)info->len) {
+            // Use the raw value of i
+            lua_pop(L, 1);
             lua_pushvalue(L, 2);
-            // Stack: [mt, key]
-            lua_gettable(L, -6);
-            return 1;
         }
+    }
+    if (! lua_isnil(L, -1)) { // Found the field name
+        // Stack: [mt, indices, i]
+        lua_getfield(L, -3, "__instances");
+        // Stack: [mt, indices, i, buckets]
+        lua_rawgeti(L, -1, info->hash);
+        // Stack: [mt, indices, i, buckets, bucket]
+        if (lua_isnil(L, -1)) {
+            luaL_error(L, "Failed to find hash bucket for hash: %p", (void*)info->hash);
+        }
+        lua_pushvalue(L, 1);
+        // Stack: [mt, indices, i, buckets, bucket, inst_udata]
+        lua_rawget(L, -2);
+        // Stack: [mt, indices, i, buckets, bucket, inst_table]
+        int i = luaL_checkinteger(L, -4);
+        lua_rawgeti(L, -1, i);
+        return 1;
     } else {
         // Fall back to class:
-        // Stack: [mt, indices, i]
+        // Stack: [mt, indices, nil]
         lua_pop(L, 2);
         // Stack: [mt]
         lua_pushvalue(L, 2);
@@ -341,11 +419,11 @@ static int Ltostring(lua_State *L)
     
     lua_getfield(L, -1, "__instances");
     // Stack: [mt, buckets]
-    lua_Integer* hash_address = (lua_Integer*)lua_touserdata(L, 1);
-    if (! hash_address) {
+    immutable_info_t *info = (immutable_info_t*)lua_touserdata(L, 1);
+    if (! info) {
         luaL_error(L, "invalid type");
     }
-    lua_rawgeti(L, -1, *hash_address);
+    lua_rawgeti(L, -1, info->hash);
     // Stack: [mt, buckets, bucket]
     if (lua_isnil(L, -1)) {
         luaL_error(L, "Failed to find hash bucket");
@@ -360,43 +438,59 @@ static int Ltostring(lua_State *L)
     int tostring_index = lua_gettop(L);
     lua_getfield(L, -5, "__fields");
     // Stack: [mt, buckets, bucket, inst_table, tostring, fields]
-    int num_fields = lua_objlen(L, -1);
-    int fields_index = lua_gettop(L);
-    
-    int needs_comma = 0;
-    for (int i = 1; i <= num_fields; i++) {
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ...]
-        if (needs_comma) {
-            luaL_addstring(&b, ", ");
-        } else {
-            needs_comma = 1;
-        }
-        lua_rawgeti(L, fields_index, i);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., fieldname]
-        if (lua_type(L, -1) == LUA_TNUMBER && lua_tointeger(L, -1) == i) {
-            lua_pop(L, 1);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ...]
-        } else {
+    if (lua_isnil(L, -1)) {
+        lua_pop(L, 1);
+        // Stack: [mt, buckets, bucket, inst_table, tostring]
+        immutable_info_t *info = (immutable_info_t*)lua_touserdata(L, 1);
+        int n = info->len;
+        int needs_comma = 0;
+        for (int i = 1; i <= n; i++) {
+            // Stack: [mt, buckets, bucket, inst_table, tostring, ???]
+            if (needs_comma) {
+                luaL_addstring(&b, ", ");
+            } else {
+                needs_comma = 1;
+            }
             lua_pushvalue(L, tostring_index);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., fieldname, tostring]
-            lua_insert(L, -2);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., tostring, fieldname]
+            // Stack: [mt, buckets, bucket, inst_table, tostring, ???, tostring]
+            lua_rawgeti(L, inst_table_index, i);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, ???, tostring, value]
             lua_call(L, 1, 1);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., field string]
+            // Stack: [mt, buckets, bucket, inst_table, tostring, ???, value string]
             luaL_addvalue(&b);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ...]
-            luaL_addstring(&b, "=");
+            // Stack: [mt, buckets, bucket, inst_table, tostring, ???]
+        }
+    } else {
+        int num_fields = lua_objlen(L, -1);
+        int fields_index = lua_gettop(L);
+        int needs_comma = 0;
+        for (int i = 1; i <= num_fields; i++) {
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???]
+            if (needs_comma) {
+                luaL_addstring(&b, ", ");
+            } else {
+                needs_comma = 1;
+            }
+            lua_pushvalue(L, tostring_index);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???, tostring]
+            lua_rawgeti(L, fields_index, i);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???, tostring, fieldname]
+            lua_call(L, 1, 1);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???, field string]
+            luaL_addvalue(&b);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???]
+            
+            luaL_addstring(&b, "=");
+
+            lua_pushvalue(L, tostring_index);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???, tostring]
+            lua_rawgeti(L, inst_table_index, i);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???, tostring, value]
+            lua_call(L, 1, 1);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???, value string]
+            luaL_addvalue(&b);
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ???]
         }
-        lua_rawgeti(L, inst_table_index, i);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., value]
-        lua_pushvalue(L, tostring_index);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., value, tostring]
-        lua_insert(L, -2);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., tostring, value]
-        lua_call(L, 1, 1);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., value string]
-        luaL_addvalue(&b);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ...]
     }
     luaL_addstring(&b, ")");
     luaL_pushresult(&b);
@@ -411,11 +505,11 @@ static int Lnexti(lua_State *L)
     // Stack: [mt]
     lua_getfield(L, -1, "__instances");
     // Stack: [mt, buckets]
-    lua_Integer* hash_address = (lua_Integer*)lua_touserdata(L, 1);
-    if (! hash_address) {
+    immutable_info_t *info = (immutable_info_t*)lua_touserdata(L, 1);
+    if (! info) {
         luaL_error(L, "invalid type");
     }
-    lua_rawgeti(L, -1, *hash_address);
+    lua_rawgeti(L, -1, info->hash);
     // Stack: [mt, buckets, bucket]
     if (lua_isnil(L, -1)) {
         luaL_error(L, "Failed to find hash bucket");
@@ -426,17 +520,30 @@ static int Lnexti(lua_State *L)
     // Stack: [mt, buckets, bucket, inst_table]
     lua_getfield(L, -4, "__fields");
     // Stack: [mt, buckets, bucket, inst_table, fields]
-    lua_pushvalue(L, 2);
-    // Stack: [mt, buckets, bucket, inst_table, fields, i]
-    if (lua_next(L, -2) == 0) {
-        return 0;
+    if (lua_isnil(L, -1)) {
+        lua_pop(L, 1);
+        // Stack: [mt, buckets, bucket, inst_table]
+        lua_pushvalue(L, 2);
+        // Stack: [mt, buckets, bucket, inst_table, i]
+        if (lua_next(L, -2) == 0) {
+            return 0;
+        } else {
+            return 2;
+        }
+    } else {
+        lua_pushvalue(L, 2);
+        // Stack: [mt, buckets, bucket, inst_table, fields, i]
+        if (lua_next(L, -2) == 0) {
+            return 0;
+        }
+        // Stack: [mt, buckets, bucket, inst_table, fields, i2, next_fieldname]
+        lua_pop(L, 1);
+        // Stack: [mt, buckets, bucket, inst_table, fields, i2]
+        int i = luaL_checkinteger(L, -1);
+        lua_rawgeti(L, -3, i);
+        // Stack: [mt, buckets, bucket, inst_table, fields, i2, value]
+        return 2;
     }
-    // Stack: [mt, buckets, bucket, inst_table, fields, i2, next_fieldname]
-    lua_pop(L, 1);
-    // Stack: [mt, buckets, bucket, inst_table, fields, i2]
-    lua_rawgeti(L, -3, lua_tonumber(L, -1));
-    // Stack: [mt, buckets, bucket, inst_table, fields, i2, value]
-    return 2;
 }
 
 static int Lipairs(lua_State *L)
@@ -458,11 +565,11 @@ static int Lnext(lua_State *L)
     // Stack: [mt]
     lua_getfield(L, -1, "__instances");
     // Stack: [mt, buckets]
-    lua_Integer* hash_address = (lua_Integer*)lua_touserdata(L, 1);
-    if (! hash_address) {
+    immutable_info_t *info = (immutable_info_t*)lua_touserdata(L, 1);
+    if (! info) {
         luaL_error(L, "invalid type");
     }
-    lua_rawgeti(L, -1, *hash_address);
+    lua_rawgeti(L, -1, info->hash);
     // Stack: [mt, buckets, bucket]
     if (lua_isnil(L, -1)) {
         luaL_error(L, "Failed to find hash bucket");
@@ -473,25 +580,37 @@ static int Lnext(lua_State *L)
     // Stack: [mt, buckets, bucket, inst_table]
     lua_getfield(L, -4, "__indices");
     // Stack: [mt, buckets, bucket, inst_table, fields]
-    lua_pushvalue(L, 2);
-    // Stack: [mt, buckets, bucket, inst_table, fields, k]
-    if (lua_next(L, -2) == 0) {
-        return 0;
+    if (lua_isnil(L, -1)) {
+        lua_pop(L, 1);
+        // Stack: [mt, buckets, bucket, inst_table]
+        lua_pushvalue(L, 2);
+        // Stack: [mt, buckets, bucket, inst_table, k]
+        if (lua_next(L, -2) == 0) {
+            return 0;
+        }
+        // Stack: [mt, buckets, bucket, inst_table, k2, value]
+        return 2;
+    } else {
+        lua_pushvalue(L, 2);
+        // Stack: [mt, buckets, bucket, inst_table, fields, k]
+        if (lua_next(L, -2) == 0) {
+            return 0;
+        }
+        // Stack: [mt, buckets, bucket, inst_table, fields, k2, next_i]
+        lua_gettable(L, -4);
+        // Stack: [mt, buckets, bucket, inst_table, fields, k2, value]
+        return 2;
     }
-    // Stack: [mt, buckets, bucket, inst_table, fields, k2, next_i]
-    lua_gettable(L, -4);
-    // Stack: [mt, buckets, bucket, inst_table, fields, k2, value]
-    return 2;
 }
 
 static int Lpairs(lua_State *L)
 {
     lua_pushcfunction(L, Lnext);
-    // Stack: [Lnexti]
+    // Stack: [Lnext]
     lua_pushvalue(L, 1);
-    // Stack: [Lnexti, inst_udata]
+    // Stack: [Lnext, inst_udata]
     lua_pushnil(L);
-    // Stack: [Lnexti, inst_udata, nil]
+    // Stack: [Lnext, inst_udata, nil]
     return 3;
 }
 
@@ -577,37 +696,8 @@ static int Lmake_class(lua_State *L)
             lua_setfield(L, -2, "__indices");
             break;
         }
-        case LUA_TNUMBER: {
-            // If no fields were passed in, make them empty (i.e. a singleton)
-            lua_Integer n = lua_tointeger(L, 1);
-            if (n < 0) {
-                luaL_error(L, "immutable table size must be positive");
-            }
-            lua_createtable(L, n, 0);
-            lua_createtable(L, n, 0);
-            // Stack: [CLS, __fields, __indices]
-            for (lua_Integer i = 1; i <= n; i++) {
-                lua_pushinteger(L, i);
-                // Stack: [CLS, __fields, __indices, i]
-                lua_rawseti(L, -2, i);
-                // Stack: [CLS, __fields, __indices]
-                lua_pushinteger(L, i);
-                // Stack: [CLS, __fields, __indices, i]
-                lua_rawseti(L, -3, i);
-                // Stack: [CLS, __fields, __indices]
-            }
-            // Stack: [CLS, __fields, __indices]
-            lua_setfield(L, -3, "__indices");
-            // Stack: [CLS, __fields]
-            lua_setfield(L, -2, "__fields");
-            break;
-        }
         case LUA_TNIL: case LUA_TNONE: {
-            // If no fields were passed in, make them empty (i.e. a singleton)
-            lua_createtable(L, 0, 0);
-            lua_setfield(L, -2, "__fields");
-            lua_createtable(L, 0, 0);
-            lua_setfield(L, -2, "__indices");
+            // If no fields were passed in, so leave __fields and __indices empty
             break;
         }
         default: {
@@ -659,5 +749,7 @@ LUALIB_API int luaopen_immutable(lua_State *L)
     lua_settable(L, LUA_REGISTRYINDEX);
 
     lua_pushcfunction(L, Lmake_class);
+    lua_pushcfunction(L, Lhash);
+    lua_setglobal(L, "extract_hash");
     return 1;
 }
diff --git a/tests.lua b/tests.lua
index 5cc32f7..c6dec3f 100644
--- a/tests.lua
+++ b/tests.lua
@@ -215,26 +215,26 @@ if _VERSION == "Lua 5.3" then
 end
 
 test("Testing immutable(n)", function()
-    local Tup3 = immutable(3, {name="Tuple"})
+    local Tup3 = immutable(nil, {name="Tuple"})
     assert(tostring(Tup3(1,2,3)) == "Tuple(1, 2, 3)")
 end)
 
 test("Testing tostring(class)", function()
-    local C1 = immutable(0, {name="MYNAME"})
+    local C1 = immutable(nil, {name="MYNAME"})
     assert(tostring(C1) == "MYNAME")
     local C2 = immutable()
     assert(tostring(C2):match("immutable type: 0x.*"))
 end)
 
 test("Testing tuple tostring", function()
-    local tup3 = immutable(3)
+    local tup3 = immutable(nil)
     assert(tostring(tup3(1,2,3)) == "(1, 2, 3)")
     assert(tostring(tup3(1,tup3(2,3,4),5)) == "(1, (2, 3, 4), 5)")
 end)
 
 test("Testing giant immutable table", function()
     local keys = {}
-    local N = 100000
+    local N = 10000
     for i=1,N do keys[i] = "key_"..tostring(i) end
     local T = immutable(keys)
     local values = {}
@@ -247,5 +247,5 @@ if num_errors == 0 then
 else
     print(bright..red.."*** "..tostring(num_errors).." test"..(num_errors > 1 and "s" or "").." failed! ***"..reset)
     io.write(reset)
-    os.exit(false, true)
+    error()
 end