diff --git a/src/docset.rs b/src/docset.rs
index 5d6b6f677..c5cb042c6 100644
--- a/src/docset.rs
+++ b/src/docset.rs
@@ -142,6 +142,11 @@ impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {
         unboxed.size_hint()
     }
 
+    fn append_to_bitset(&mut self, bitset: &mut BitSet) {
+        let unboxed: &mut TDocSet = self.borrow_mut();
+        unboxed.append_to_bitset(bitset);
+    }
+
     fn count(&mut self, delete_bitset: &DeleteBitSet) -> u32 {
         let unboxed: &mut TDocSet = self.borrow_mut();
         unboxed.count(delete_bitset)
@@ -151,9 +156,4 @@ impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {
         let unboxed: &mut TDocSet = self.borrow_mut();
         unboxed.count_including_deleted()
     }
-
-    fn append_to_bitset(&mut self, bitset: &mut BitSet) {
-        let unboxed: &mut TDocSet = self.borrow_mut();
-        unboxed.append_to_bitset(bitset);
-    }
 }
diff --git a/src/query/union.rs b/src/query/union.rs
index f636f0576..94ab7be73 100644
--- a/src/query/union.rs
+++ b/src/query/union.rs
@@ -250,6 +250,22 @@ where
     fn size_hint(&self) -> u32 {
         0u32
     }
+
+    fn for_each(&mut self, callback: &mut FnMut(DocId, Score)) {
+        // TODO how do we deal with the fact that people may have called .advance() before.
+        while self.refill() {
+            let offset = self.offset;
+            for cursor in 0..HORIZON_NUM_TINYBITSETS {
+                while let Some(val) = self.bitsets[cursor].pop_lowest() {
+                    let delta = val + (cursor as u32) * 64;
+                    let doc = offset + delta;
+                    let score_combiner = &mut self.scores[delta as usize];
+                    let score = score_combiner.score();
+                    score_combiner.clear();
+                }
+            }
+        }
+    }
 }
 
 impl<TScorer, TScoreCombiner> Scorer for Union<TScorer, TScoreCombiner>