docs/attachments/LUCENE-8558/LUCENE-8558.patch

diff --git a/lucene/core/src/java/org/apache/lucene/codecs/perfield/PerFieldMergeState.java b/lucene/core/src/java/org/apache/lucene/codecs/perfield/PerFieldMergeState.java
index 291a384608..99a04da042 100644
--- a/lucene/core/src/java/org/apache/lucene/codecs/perfield/PerFieldMergeState.java
+++ b/lucene/core/src/java/org/apache/lucene/codecs/perfield/PerFieldMergeState.java
@@ -125,7 +125,7 @@ final class PerFieldMergeState {
       this.filteredNames = new HashSet<>(filterFields);
       this.filtered = new ArrayList<>(filterFields.size());
       for (FieldInfo fi : src) {
-        if (filterFields.contains(fi.name)) {
+        if (this.filteredNames.contains(fi.name)) {
           this.filtered.add(fi);
           hasVectors |= fi.hasVectors();
           hasProx |= fi.getIndexOptions().compareTo(IndexOptions.DOCS_AND_FREQS_AND_POSITIONS) >= 0;