diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index b2dbfba08a1..3c8120e033d 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -418,6 +418,9 @@ Bug Fixes
 * LUCENE-10026: Fix CombinedFieldQuery equals and hashCode, which ensures
   query rewrites don't drop CombinedFieldQuery clauses. (Julie Tibshirani)
 
+* LUCENE-10039: Correct CombinedFieldQuery scoring when there is a single
+  field. (Julie Tibshirani)
+
 Other
 ---------------------
 (No changes)
diff --git a/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/CombinedFieldQuery.java b/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/CombinedFieldQuery.java
index ffb9d13f1f9..c4e00eabdcf 100644
--- a/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/CombinedFieldQuery.java
+++ b/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/CombinedFieldQuery.java
@@ -254,8 +254,7 @@ public final class CombinedFieldQuery extends Query implements Accountable {
 
   @Override
   public Query rewrite(IndexReader reader) throws IOException {
-    // optimize zero and single field cases
-    if (terms.length == 0) {
+    if (terms.length == 0 || fieldAndWeights.isEmpty()) {
       return new BooleanQuery.Builder().build();
     }
     return this;
@@ -383,14 +382,9 @@ public final class CombinedFieldQuery extends Query implements Accountable {
       if (scorer != null) {
         int newDoc = scorer.iterator().advance(doc);
         if (newDoc == doc) {
-          final float freq;
-          if (scorer instanceof CombinedFieldScorer) {
-            freq = ((CombinedFieldScorer) scorer).freq();
-          } else {
-            assert scorer instanceof TermScorer;
-            freq = ((TermScorer) scorer).freq();
-          }
-          final MultiNormsLeafSimScorer docScorer =
+          assert scorer instanceof CombinedFieldScorer;
+          float freq = ((CombinedFieldScorer) scorer).freq();
+          MultiNormsLeafSimScorer docScorer =
               new MultiNormsLeafSimScorer(
                   simWeight, context.reader(), fieldAndWeights.values(), true);
           Explanation freqExplanation = Explanation.match(freq, "termFreq=" + freq);
@@ -423,13 +417,7 @@ public final class CombinedFieldQuery extends Query implements Accountable {
         return null;
       }
 
-      // we must optimize this case (term not in segment), disjunctions require >= 2 subs
-      if (iterators.size() == 1) {
-        final LeafSimScorer scoringSimScorer =
-            new LeafSimScorer(simWeight, context.reader(), fields.get(0).field, true);
-        return new TermScorer(this, iterators.get(0), scoringSimScorer);
-      }
-      final MultiNormsLeafSimScorer scoringSimScorer =
+      MultiNormsLeafSimScorer scoringSimScorer =
           new MultiNormsLeafSimScorer(simWeight, context.reader(), fields, true);
       LeafSimScorer nonScoringSimScorer =
           new LeafSimScorer(simWeight, context.reader(), "pseudo_field", false);
diff --git a/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/MultiNormsLeafSimScorer.java b/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/MultiNormsLeafSimScorer.java
index f2c6120cff4..ba1d69a8b16 100644
--- a/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/MultiNormsLeafSimScorer.java
+++ b/lucene/sandbox/src/java/org/apache/lucene/sandbox/search/MultiNormsLeafSimScorer.java
@@ -71,8 +71,6 @@ final class MultiNormsLeafSimScorer {
 
       if (normsList.isEmpty()) {
         norms = null;
-      } else if (normsList.size() == 1) {
-        norms = normsList.get(0);
       } else {
         final NumericDocValues[] normsArr = normsList.toArray(new NumericDocValues[0]);
         final float[] weightArr = new float[normsList.size()];
diff --git a/lucene/sandbox/src/test/org/apache/lucene/sandbox/search/TestCombinedFieldQuery.java b/lucene/sandbox/src/test/org/apache/lucene/sandbox/search/TestCombinedFieldQuery.java
index 77aa9ed73ff..7798a2a7017 100644
--- a/lucene/sandbox/src/test/org/apache/lucene/sandbox/search/TestCombinedFieldQuery.java
+++ b/lucene/sandbox/src/test/org/apache/lucene/sandbox/search/TestCombinedFieldQuery.java
@@ -319,6 +319,47 @@ public class TestCombinedFieldQuery extends LuceneTestCase {
     dir.close();
   }
 
+  public void testCopyFieldWithSingleField() throws IOException {
+    Directory dir = new MMapDirectory(createTempDir());
+    Similarity similarity = randomCompatibleSimilarity();
+
+    IndexWriterConfig iwc = new IndexWriterConfig();
+    iwc.setSimilarity(similarity);
+    RandomIndexWriter w = new RandomIndexWriter(random(), dir, iwc);
+
+    int boost = Math.max(1, random().nextInt(5));
+    int numMatch = atLeast(10);
+    for (int i = 0; i < numMatch; i++) {
+      Document doc = new Document();
+      int freqA = random().nextInt(5) + 1;
+      for (int j = 0; j < freqA; j++) {
+        doc.add(new TextField("a", "foo", Store.NO));
+      }
+
+      int freqB = freqA * boost;
+      for (int j = 0; j < freqB; j++) {
+        doc.add(new TextField("b", "foo", Store.NO));
+      }
+
+      w.addDocument(doc);
+    }
+
+    IndexReader reader = w.getReader();
+    IndexSearcher searcher = newSearcher(reader);
+    searcher.setSimilarity(similarity);
+    CombinedFieldQuery query =
+        new CombinedFieldQuery.Builder()
+            .addField("a", (float) boost)
+            .addTerm(new BytesRef("foo"))
+            .build();
+
+    checkExpectedHits(searcher, numMatch, query, new TermQuery(new Term("b", "foo")));
+
+    reader.close();
+    w.close();
+    dir.close();
+  }
+
   public void testCopyFieldWithMissingFields() throws IOException {
     Directory dir = new MMapDirectory(createTempDir());
     Similarity similarity = randomCompatibleSimilarity();