diff --git a/lobject.c b/lobject.c
index 4fe5fdb4..fd522394 100644
--- a/lobject.c
+++ b/lobject.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lobject.c,v 2.14 2005/05/20 15:53:42 roberto Exp roberto $
+** $Id: lobject.c,v 2.15 2005/05/31 14:25:18 roberto Exp roberto $
 ** Some generic functions over Lua objects
 ** See Copyright Notice in lua.h
 */
@@ -116,7 +116,9 @@ const char *luaO_pushvfstring (lua_State *L, const char *fmt, va_list argp) {
     incr_top(L);
     switch (*(e+1)) {
       case 's': {
-        pushstr(L, va_arg(argp, char *));
+        const char *s = va_arg(argp, char *);
+        if (s == NULL) s = "(null)";
+        pushstr(L, s);
         break;
       }
       case 'c': {
diff --git a/ltablib.c b/ltablib.c
index 804999e2..578c1264 100644
--- a/ltablib.c
+++ b/ltablib.c
@@ -1,5 +1,5 @@
 /*
-** $Id: ltablib.c,v 1.30 2005/05/16 21:19:00 roberto Exp roberto $
+** $Id: ltablib.c,v 1.31 2005/05/17 19:49:15 roberto Exp roberto $
 ** Library for Table Manipulation
 ** See Copyright Notice in lua.h
 */
@@ -109,7 +109,7 @@ static int tremove (lua_State *L) {
 }
 
 
-static int str_concat (lua_State *L) {
+static int tconcat (lua_State *L) {
   luaL_Buffer b;
   size_t lsep;
   const char *sep = luaL_optlstring(L, 2, "", &lsep);
@@ -237,7 +237,7 @@ static int sort (lua_State *L) {
 
 
 static const luaL_reg tab_funcs[] = {
-  {"concat", str_concat},
+  {"concat", tconcat},
   {"foreach", foreach},
   {"foreachi", foreachi},
   {"getn", getn},