--- builtin.py	2011-01-20 14:02:55.000000000 -0500
+++ builtin.py.new	2011-01-20 14:02:51.000000000 -0500
@@ -147,6 +147,16 @@

 def builtin_isinstance(s_obj, s_type, variables=None):
     r = SomeBool()
+
+    if isinstance(s_type, SomeTuple):
+        for t in s_type.items:
+            r = builtin_isinstance(s_obj, t, variables)
+            if r.const:
+                return r
+
+        r.const = False
+        return r
+
     if s_type.is_constant():
         typ = s_type.const
         if issubclass(typ, pypy.rlib.rarithmetic.base_int):