diff --git a/lucene/src/test/org/apache/lucene/search/function/TestValueSource.java b/lucene/src/test/org/apache/lucene/search/function/TestValueSource.java
index 131d1a322dc..f2d314c0fb2 100644
--- a/lucene/src/test/org/apache/lucene/search/function/TestValueSource.java
+++ b/lucene/src/test/org/apache/lucene/search/function/TestValueSource.java
@@ -30,6 +30,7 @@ public class TestValueSource extends LuceneTestCase {
   public void testMultiValueSource() throws Exception {
     Directory dir = newDirectory();
     IndexWriter w = new IndexWriter(dir, new IndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(random)).setMergePolicy(newLogMergePolicy()));
+    ((LogMergePolicy) w.getConfig().getMergePolicy()).setMergeFactor(_TestUtil.nextInt(random, 2, 16));
     Document doc = new Document();
     Field f = newField("field", "", Field.Store.NO, Field.Index.NOT_ANALYZED);
     doc.add(f);