diff --git a/src/allmydata/test/test_util.py b/src/allmydata/test/test_util.py
index 575a7a493..f6a6f2ff2 100644
--- a/src/allmydata/test/test_util.py
+++ b/src/allmydata/test/test_util.py
@@ -1119,16 +1119,13 @@ class DictUtil(unittest.TestCase):
         ds.discard(2, "c")
         self.failIf(2 in ds)
 
-        ds.union(1, ["a", "e"])
-        ds.union(3, ["f"])
-        self.failUnlessEqual(ds[1], set(["a","e"]))
-        self.failUnlessEqual(ds[3], set(["f"]))
+        ds.add(3, "f")
         ds2 = dictutil.DictOfSets()
         ds2.add(3, "f")
         ds2.add(3, "g")
         ds2.add(4, "h")
         ds.update(ds2)
-        self.failUnlessEqual(ds[1], set(["a","e"]))
+        self.failUnlessEqual(ds[1], set(["a"]))
         self.failUnlessEqual(ds[3], set(["f", "g"]))
         self.failUnlessEqual(ds[4], set(["h"]))
 
diff --git a/src/allmydata/util/dictutil.py b/src/allmydata/util/dictutil.py
index 8de136f28..7c03159c6 100644
--- a/src/allmydata/util/dictutil.py
+++ b/src/allmydata/util/dictutil.py
@@ -40,15 +40,12 @@ class DictOfSets(dict):
         else:
             self[key] = set([value])
 
-    def union(self, key, values):
-        if key in self:
-            self[key].update(values)
-        else:
-            self[key] = set(values)
-
     def update(self, otherdictofsets):
-        for key, value in otherdictofsets.iteritems():
-            self.union(key, value)
+        for key, values in otherdictofsets.iteritems():
+            if key in self:
+                self[key].update(values)
+            else:
+                self[key] = set(values)
 
     def discard(self, key, value):
         if not key in self: