diff --git a/src/query/union/buffered_union.rs b/src/query/union/buffered_union.rs
index b9a0bdedc..91f0c8ee4 100644
--- a/src/query/union/buffered_union.rs
+++ b/src/query/union/buffered_union.rs
@@ -17,7 +17,9 @@ const HORIZON: u32 = 64u32 * 64u32;
 //
 // Elements are dropped and not yielded.
 fn unordered_drain_filter<T, P>(v: &mut Vec<T>, mut predicate: P)
-where P: FnMut(&mut T) -> bool {
+where
+    P: FnMut(&mut T) -> bool,
+{
     let mut i = 0;
     while i < v.len() {
         if predicate(&mut v[i]) {
@@ -143,7 +145,7 @@ impl<TScorer: Scorer, TScoreCombiner: ScoreCombiner> BufferedUnionScorer<TScorer
     }
 
     fn is_in_horizon(&self, target: DocId) -> bool {
-        let gap = target - self.offset;
+        let gap = target - self.window_start_doc;
         gap < HORIZON
     }
 }