1 files changed, 13 insertions, 2 deletions

diff --git a/lbaselib.c b/lbaselib.c
index 1d60c9de..5a23c937 100644
--- a/lbaselib.c
+++ b/lbaselib.c
@@ -337,9 +337,20 @@ static int load_aux (lua_State *L, int status, int envidx) {
 }
 
 
+static const char *getmode (lua_State *L, int idx) {
+  const char *mode = luaL_optstring(L, idx, "bt");
+  int i = 0;
+  if (mode[i] == 'b') i++;
+  if (mode[i] == 't') i++;
+  if (mode[i] != '\0')
+    luaL_argerror(L, idx, "invalid mode");
+  return mode;
+}
+
+
 static int luaB_loadfile (lua_State *L) {
   const char *fname = luaL_optstring(L, 1, NULL);
-  const char *mode = luaL_optstring(L, 2, NULL);
+  const char *mode = getmode(L, 2);
   int env = (!lua_isnone(L, 3) ? 3 : 0);  /* 'env' index or 0 if no 'env' */
   int status = luaL_loadfilex(L, fname, mode);
   return load_aux(L, status, env);
@@ -388,7 +399,7 @@ static int luaB_load (lua_State *L) {
   int status;
   size_t l;
   const char *s = lua_tolstring(L, 1, &l);
-  const char *mode = luaL_optstring(L, 3, "bt");
+  const char *mode = getmode(L, 3);
   int env = (!lua_isnone(L, 4) ? 4 : 0);  /* 'env' index or 0 if no 'env' */
   if (s != NULL) {  /* loading a string? */
     const char *chunkname = luaL_optstring(L, 2, s);