@@ -638,14 +638,18 @@ static const char *funcnamefromcode (lua_State *L, CallInfo *ci,
 
 
 /*
-** The subtraction of two potentially unrelated pointers is
-** not ISO C, but it should not crash a program; the subsequent
-** checks are ISO C and ensure a correct result.
+** Check whether pointer 'o' points to some value in the stack
+** frame of the current function. Because 'o' may not point to a
+** value in this stack, we cannot compare it with the region
+** boundaries (undefined behaviour in ISO C).
 */
 static int isinstack (CallInfo *ci, const TValue *o) {
-  StkId base = ci->func + 1;
-  ptrdiff_t i = cast(StkId, o) - base;
-  return (0 <= i && i < (ci->top - base) && s2v(base + i) == o);
+  StkId pos;
+  for (pos = ci->func + 1; pos < ci->top; pos++) {
+    if (o == s2v(pos))
+      return 1;
+  }
+  return 0;  /* not found */
 }
 
 
 
@@ -191,6 +191,13 @@ checkmessage("a = 24 // 0", "divide by zero")
 checkmessage("a = 1 % 0", "'n%0'")
 
 
+-- type error for an object which is neither in an upvalue nor a register.
+-- The following code will try to index the value 10 that is stored in
+-- the metatable, without moving it to a register.
+checkmessage("local a = setmetatable({}, {__index = 10}).x",
+             "attempt to index a number value")
+
+
 -- numeric for loops
 checkmessage("for i = {}, 10 do end", "table")
 checkmessage("for i = io.stdin, 10 do end", "FILE")