1 files changed, 4 insertions, 2 deletions

diff --git a/lstrlib.c b/lstrlib.c
index 41ebc523..ab4258e5 100644
--- a/lstrlib.c
+++ b/lstrlib.c
@@ -181,7 +181,7 @@ static int str_byte (lua_State *L) {
   size_t pose = getendpos(L, 3, pi, l);
   int n, i;
   if (posi > pose) return 0;  /* empty interval; return no values */
-  if (pose - posi >= INT_MAX)  /* arithmetic overflow? */
+  if (pose - posi >= (size_t)INT_MAX)  /* arithmetic overflow? */
     return luaL_error(L, "string slice too long");
   n = (int)(pose -  posi) + 1;
   luaL_checkstack(L, n, "string slice too long");
@@ -1159,7 +1159,7 @@ static int str_format (lua_State *L) {
       char *buff = luaL_prepbuffsize(&b, MAX_ITEM);  /* to put formatted item */
       int nb = 0;  /* number of bytes in added item */
       if (++arg > top)
-        luaL_argerror(L, arg, "no value");
+        return luaL_argerror(L, arg, "no value");
       strfrmt = scanformat(L, strfrmt, form);
       switch (*strfrmt++) {
         case 'c': {
@@ -1186,6 +1186,8 @@ static int str_format (lua_State *L) {
           break;
         }
         case 'q': {
+          if (form[2] != '\0')  /* modifiers? */
+            return luaL_error(L, "specifier '%%q' cannot have modifiers");
           addliteral(L, &b, arg);
           break;
         }