--- old-tahoe-1.8/src/allmydata/util/spans.py	2010-08-16 22:34:18.267000000 +0100
+++ new-tahoe-1.8/src/allmydata/util/spans.py	2010-08-16 22:34:18.470000000 +0100
@@ -255,7 +255,12 @@
 
     def get_spans(self):
         """Return a Spans object with a bit set for each byte I hold"""
-        return Spans([(start, len(data)) for (start,data) in self.spans])
+        # XXX This is not the right long-term fix, because it depends on an undocumented
+        # invariant of Spans.
+        s = Spans()
+        s._spans = [(start, len(data)) for (start,data) in self.spans]
+        s._check()
+        return s
 
     def assert_invariants(self):
         if not self.spans: