diff --git a/lstrlib.c b/lstrlib.c
index cd10c320..6c8e1ba4 100644
--- a/lstrlib.c
+++ b/lstrlib.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lstrlib.c,v 1.141 2008/06/12 14:21:18 roberto Exp roberto $
+** $Id: lstrlib.c,v 1.142 2009/02/03 19:39:19 roberto Exp roberto $
 ** Standard library for string operations and pattern-matching
 ** See Copyright Notice in lua.h
 */
@@ -777,14 +777,13 @@ static int str_format (lua_State *L) {
           sprintf(buff, form, (int)luaL_checknumber(L, arg));
           break;
         }
-        case 'd':  case 'i': {
-          addintlen(form);
-          sprintf(buff, form, (LUA_INTFRM_T)luaL_checknumber(L, arg));
-          break;
-        }
+        case 'd':  case 'i':
         case 'o':  case 'u':  case 'x':  case 'X': {
+          lua_Number n = luaL_checknumber(L, arg);
+          LUA_INTFRM_T r = (n < 0) ? (LUA_INTFRM_T)n :
+                                     (LUA_INTFRM_T)(unsigned LUA_INTFRM_T)n;
           addintlen(form);
-          sprintf(buff, form, (unsigned LUA_INTFRM_T)luaL_checknumber(L, arg));
+          sprintf(buff, form, r);
           break;
         }
         case 'e':  case 'E': case 'f':