Ensure bysetpos is in an acceptable range.
diff --git a/test.py b/test.py
index 734979c..ff67105 100644
--- a/test.py
+++ b/test.py
@@ -2933,6 +2933,19 @@
                           datetime(1998, 1, 6, 9, 0),
                           datetime(1998, 12, 31, 9, 0)])
 
+    def testBadBySetPos(self):
+        self.assertRaises(ValueError,
+                          rrule, MONTHLY,
+                                 count=1,
+                                 bysetpos=0,
+                                 dtstart=parse("19970902T090000"))
+
+    def testBadBySetPosMany(self):
+        self.assertRaises(ValueError,
+                          rrule, MONTHLY,
+                                 count=1,
+                                 bysetpos=(-1,0,1),
+                                 dtstart=parse("19970902T090000"))
 
 
 class ParserTest(unittest.TestCase):