diff --git a/pysam/libctabixproxies.pyx b/pysam/libctabixproxies.pyx
index 9b81af16..152c3c3e 100644
--- a/pysam/libctabixproxies.pyx
+++ b/pysam/libctabixproxies.pyx
@@ -365,14 +365,14 @@ cdef class NamedTupleProxy(TupleProxy):
         '''set attribute.'''
         cdef int idx
         idx, f = self.map_key2field[key]
-        if self.nfields < idx:
+        if idx >= self.nfields:
             raise KeyError("field %s not set" % key)
         TupleProxy.__setitem__(self, idx, str(value))
 
     def __getattr__(self, key):
         cdef int idx
         idx, f = self.map_key2field[key]
-        if self.nfields < idx:
+        if idx >= self.nfields:
             raise KeyError("field %s not set" % key)
         if f == str:
             return force_str(self.fields[idx],
diff --git a/tests/tabix_test.py b/tests/tabix_test.py
index 33c3e708..d82379d1 100644
--- a/tests/tabix_test.py
+++ b/tests/tabix_test.py
@@ -501,6 +501,9 @@ def testRead(self):
             self.assertEqual(c[0], r.contig)
             self.assertEqual(int(c[1]), r.start)
             self.assertEqual(int(c[2]), r.end)
+            # Needs lambda so that the property getter isn't called too soon
+            self.assertRaises(KeyError, lambda: r.name)
+            self.assertRaises(KeyError, lambda: r.score)
             self.assertEqual(list(c), list(r))
             self.assertEqual("\t".join(map(str, c)),
                              str(r))
@@ -524,6 +527,12 @@ def testWrite(self):
             self.assertEqual(int(c[2]) + 1, r.end)
             self.assertEqual(str(int(c[2]) + 1), r[2])
 
+            with self.assertRaises(IndexError):
+                r.name = "test"
+
+            with self.assertRaises(IndexError):
+                r.score = 1
+
 
 class TestVCF(unittest.TestCase):