diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 02d25d1d406..7f90a7e1480 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -14,7 +14,12 @@ Changes in Runtime Behavior
 
 
 ======================= Lucene 7.2.0 =======================
-(No Changes)
+
+Bug Fixes
+
+* LUCENE-7991: KNearestNeighborDocumentClassifier.knnSearch no longer applies
+  a previous boosted field's factor to subsequent unboosted fields.
+  (Christine Poerschke)
 
 ======================= Lucene 7.1.0 =======================
 
diff --git a/lucene/classification/src/java/org/apache/lucene/classification/document/KNearestNeighborDocumentClassifier.java b/lucene/classification/src/java/org/apache/lucene/classification/document/KNearestNeighborDocumentClassifier.java
index 88d41fcd8d2..d687722c87c 100644
--- a/lucene/classification/src/java/org/apache/lucene/classification/document/KNearestNeighborDocumentClassifier.java
+++ b/lucene/classification/src/java/org/apache/lucene/classification/document/KNearestNeighborDocumentClassifier.java
@@ -129,6 +129,7 @@ public class KNearestNeighborDocumentClassifier extends KNearestNeighborClassifi
       for (String fieldContent : fieldValues) {
         mltQuery.add(new BooleanClause(mlt.like(fieldName, new StringReader(fieldContent)), BooleanClause.Occur.SHOULD));
       }
+      mlt.setBoostFactor(1);// restore neutral boost for next field
     }
     Query classFieldQuery = new WildcardQuery(new Term(classFieldName, "*"));
     mltQuery.add(new BooleanClause(classFieldQuery, BooleanClause.Occur.MUST));