diff --git a/ldump.c b/ldump.c
index aca6245b..c4475576 100644
--- a/ldump.c
+++ b/ldump.c
@@ -198,11 +198,9 @@ static void DumpFunction (const Proto *f, TString *psource, DumpState *D) {
 
 static void DumpHeader (DumpState *D) {
   DumpLiteral(LUA_SIGNATURE, D);
-  DumpByte(LUAC_VERSION, D);
+  DumpInt(LUAC_VERSION, D);
   DumpByte(LUAC_FORMAT, D);
   DumpLiteral(LUAC_DATA, D);
-  DumpByte(sizeof(int), D);
-  DumpByte(sizeof(size_t), D);
   DumpByte(sizeof(Instruction), D);
   DumpByte(sizeof(lua_Integer), D);
   DumpByte(sizeof(lua_Number), D);
diff --git a/lundump.c b/lundump.c
index 00ff6def..a6004933 100644
--- a/lundump.c
+++ b/lundump.c
@@ -10,6 +10,7 @@
 #include "lprefix.h"
 
 
+#include <limits.h>
 #include <string.h>
 
 #include "lua.h"
@@ -37,7 +38,7 @@ typedef struct {
 
 
 static l_noret error (LoadState *S, const char *why) {
-  luaO_pushfstring(S->L, "%s: %s precompiled chunk", S->name, why);
+  luaO_pushfstring(S->L, "%s: bad binary format (%s)", S->name, why);
   luaD_throw(S->L, LUA_ERRSYNTAX);
 }
 
@@ -50,7 +51,7 @@ static l_noret error (LoadState *S, const char *why) {
 
 static void LoadBlock (LoadState *S, void *b, size_t size) {
   if (luaZ_read(S->Z, b, size) != 0)
-    error(S, "truncated");
+    error(S, "truncated chunk");
 }
 
 
@@ -60,24 +61,32 @@ static void LoadBlock (LoadState *S, void *b, size_t size) {
 static lu_byte LoadByte (LoadState *S) {
   int b = zgetc(S->Z);
   if (b == EOZ)
-    error(S, "truncated");
+    error(S, "truncated chunk");
   return cast_byte(b);
 }
 
 
-static size_t LoadSize (LoadState *S) {
+static size_t LoadUnsigned (LoadState *S, size_t limit) {
   size_t x = 0;
   int b;
+  limit >>= 7;
   do {
     b = LoadByte(S);
+    if (x >= limit)
+      error(S, "integer overflow");
     x = (x << 7) | (b & 0x7f);
   } while ((b & 0x80) == 0);
   return x;
 }
 
 
+static size_t LoadSize (LoadState *S) {
+  return LoadUnsigned(S, ~(size_t)0);
+}
+
+
 static int LoadInt (LoadState *S) {
-  return cast_int(LoadSize(S));
+  return cast_int(LoadUnsigned(S, INT_MAX));
 }
 
 
@@ -255,28 +264,27 @@ static void checkliteral (LoadState *S, const char *s, const char *msg) {
 
 static void fchecksize (LoadState *S, size_t size, const char *tname) {
   if (LoadByte(S) != size)
-    error(S, luaO_pushfstring(S->L, "%s size mismatch in", tname));
+    error(S, luaO_pushfstring(S->L, "%s size mismatch", tname));
 }
 
 
 #define checksize(S,t)	fchecksize(S,sizeof(t),#t)
 
 static void checkHeader (LoadState *S) {
-  checkliteral(S, LUA_SIGNATURE + 1, "not a");  /* 1st char already checked */
-  if (LoadByte(S) != LUAC_VERSION)
-    error(S, "version mismatch in");
+  /* 1st char already checked */
+  checkliteral(S, LUA_SIGNATURE + 1, "not a binary chunk");
+  if (LoadInt(S) != LUAC_VERSION)
+    error(S, "version mismatch");
   if (LoadByte(S) != LUAC_FORMAT)
-    error(S, "format mismatch in");
-  checkliteral(S, LUAC_DATA, "corrupted");
-  checksize(S, int);
-  checksize(S, size_t);
+    error(S, "format mismatch");
+  checkliteral(S, LUAC_DATA, "corrupted chunk");
   checksize(S, Instruction);
   checksize(S, lua_Integer);
   checksize(S, lua_Number);
   if (LoadInteger(S) != LUAC_INT)
-    error(S, "endianness mismatch in");
+    error(S, "integer format mismatch");
   if (LoadNumber(S) != LUAC_NUM)
-    error(S, "float format mismatch in");
+    error(S, "float format mismatch");
 }
 
 
diff --git a/lundump.h b/lundump.h
index 739c7fcd..5b05fed4 100644
--- a/lundump.h
+++ b/lundump.h
@@ -18,8 +18,7 @@
 #define LUAC_INT	0x5678
 #define LUAC_NUM	cast_num(370.5)
 
-#define MYINT(s)	(s[0]-'0')
-#define LUAC_VERSION	(MYINT(LUA_VERSION_MAJOR)*16+MYINT(LUA_VERSION_MINOR))
+#define LUAC_VERSION	LUA_VERSION_NUM
 #define LUAC_FORMAT	0	/* this is the official format */
 
 /* load one chunk; from lundump.c */
diff --git a/testes/calls.lua b/testes/calls.lua
index f5108a47..941493b1 100644
--- a/testes/calls.lua
+++ b/testes/calls.lua
@@ -397,17 +397,15 @@ assert((function (a) return a end)() == nil)
 
 print("testing binary chunks")
 do
-  local header = string.pack("c4BBc6BBBBBj",
-    "\27Lua",                -- signature
-    5*16 + 4,                -- version 5.4
-    0,                       -- format
-    "\x19\x93\r\n\x1a\n",    -- data
-    string.packsize("i"),    -- sizeof(int)
-    string.packsize("T"),    -- sizeof(size_t)
-    4,                       -- size of instruction
-    string.packsize("j"),    -- sizeof(lua integer)
-    string.packsize("n"),    -- sizeof(lua number)
-    0x5678                   -- LUAC_INT
+  local header = string.pack("c4BBBc6BBBj",
+    "\27Lua",                                  -- signature
+    (504 >> 7) & 0x7f, (504 & 0x7f) | 0x80,    -- version 5.4 (504)
+    0,                                         -- format
+    "\x19\x93\r\n\x1a\n",                      -- data
+    4,                                         -- size of instruction
+    string.packsize("j"),                      -- sizeof(lua integer)
+    string.packsize("n"),                      -- sizeof(lua number)
+    0x5678                                     -- LUAC_INT
     -- LUAC_NUM may not have a unique binary representation (padding...)
   )
   local c = string.dump(function () local a = 1; local b = 3; return a+b*3 end)