diff --git a/limmutable.c b/limmutable.c
index c58bf9b..6a60325 100644
--- a/limmutable.c
+++ b/limmutable.c
@@ -19,8 +19,6 @@
 // The C API changed from 5.1 to 5.2, so these shims help the code compile on >=5.2
 #if LUA_VERSION_NUM >= 502
 #define lua_objlen(L, i) lua_rawlen(L, i)
-#define lua_equal(L, i, j) lua_compare(L, i, j, LUA_OPEQ)
-#define luaH_getnum(t, k) luaH_getint(t, k)
 #define luaL_register(L, _, R) luaL_setfuncs(L, R, 0)
 #endif
 
@@ -182,6 +180,10 @@ 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!");
+    }
     // Stack: [mt, fields]
     lua_pushnil(L);
     int num_args = 0;
@@ -323,47 +325,50 @@ static int Ltostring(lua_State *L)
     lua_pushvalue(L, 1);
     // Stack: [mt, buckets, bucket, inst_udata]
     lua_rawget(L, -2);
+    int inst_table_index = lua_absindex(L, -1);
     // Stack: [mt, buckets, bucket, inst_table]
     lua_getglobal(L, "tostring");
     // Stack: [mt, buckets, bucket, inst_table, tostring]
+    int tostring_index = lua_absindex(L, -1);
     lua_getfield(L, -5, "__fields");
     // Stack: [mt, buckets, bucket, inst_table, tostring, fields]
+    int num_fields = lua_objlen(L, -1);
+    int fields_index = lua_absindex(L, -1);
     
-    lua_pushnil(L);
     int needs_comma = 0;
-    int numeric_index = 1;
-    while (lua_next(L, -2) != 0) {
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, fieldname]
+    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;
         }
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, fieldname]
-        if (lua_type(L, -1) == LUA_TNUMBER && lua_tointeger(L, -1) == numeric_index) {
+        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 {
-            lua_pushvalue(L, -4);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, fieldname, tostring]
+            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, i, tostring, fieldname]
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., tostring, fieldname]
             lua_call(L, 1, 1);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, field string]
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., field string]
             luaL_addvalue(&b);
-            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i]
+            // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ...]
             luaL_addstring(&b, "=");
         }
-        lua_rawgeti(L, -4, lua_tonumber(L, -1));
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, value]
-        lua_pushvalue(L, -4);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, value, tostring]
+        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, i, tostring, value]
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., tostring, value]
         lua_call(L, 1, 1);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i, value string]
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ..., value string]
         luaL_addvalue(&b);
-        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, i]
-        numeric_index++;
+        // Stack: [mt, buckets, bucket, inst_table, tostring, fields, ...]
     }
     luaL_addstring(&b, ")");
     luaL_pushresult(&b);
diff --git a/tests.lua b/tests.lua
index d73373a..4024ace 100644
--- a/tests.lua
+++ b/tests.lua
@@ -26,13 +26,13 @@ local function test(description, fn)
     io.write(red)
     local ok, err = pcall(fn)
     if not ok then
-        io.write(reset..dim.."\r..................................")
+        io.write(reset..dim.."\r....................................")
         io.write(reset.."["..bright..red.."FAILED"..reset.."]\r")
         io.write("\r"..description.."\n"..reset)
         print(reset..red..(err or "")..reset)
         num_errors = num_errors + 1
     else
-        io.write(reset..dim.."\r..................................")
+        io.write(reset..dim.."\r....................................")
         io.write(reset.."["..green.."PASSED"..reset.."]\r")
         io.write(description.."\n")
     end
@@ -218,6 +218,22 @@ test("Testing tostring(class)", function()
     assert(tostring(C2):match("immutable type: 0x.*"))
 end)
 
+test("Testing tuple tostring", function()
+    local tup3 = immutable(3)
+    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
+    for i=1,N do keys[i] = "key_"..tostring(i) end
+    local T = immutable(keys)
+    local values = {}
+    for i,key in ipairs(keys) do values[key] = i*i end
+    assert(T:from_table(values))
+end)
+
 if num_errors == 0 then
     print(green.."All tests passed!"..reset)
 else