diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 05d99b76911..0c6b96af9c6 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -187,6 +187,8 @@ Other
 * LUCENE-8993, LUCENE-8807: Changed all repository and download references in build files
   to HTTPS. (Uwe Schindler)
 
+* LUCENE-8998: Fix OverviewImplTest.testIsOptimized reproducible failure. (Tomoko Uchida)
+
 ======================= Lucene 8.2.0 =======================
 
 API Changes
diff --git a/lucene/luke/src/test/org/apache/lucene/luke/models/overview/OverviewTestBase.java b/lucene/luke/src/test/org/apache/lucene/luke/models/overview/OverviewTestBase.java
index 5554d709941..f1516174250 100644
--- a/lucene/luke/src/test/org/apache/lucene/luke/models/overview/OverviewTestBase.java
+++ b/lucene/luke/src/test/org/apache/lucene/luke/models/overview/OverviewTestBase.java
@@ -28,6 +28,8 @@ import org.apache.lucene.document.Field;
 import org.apache.lucene.document.TextField;
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.NoMergePolicy;
 import org.apache.lucene.index.RandomIndexWriter;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.LuceneTestCase;
@@ -55,7 +57,9 @@ public abstract class OverviewTestBase extends LuceneTestCase {
     Path indexDir = createTempDir();
 
     Directory dir = newFSDirectory(indexDir);
-    RandomIndexWriter writer = new RandomIndexWriter(random(), dir, new MockAnalyzer(random()));
+    IndexWriterConfig config = new IndexWriterConfig(new MockAnalyzer(random()));
+    config.setMergePolicy(NoMergePolicy.INSTANCE);  // see LUCENE-8998
+    RandomIndexWriter writer = new RandomIndexWriter(random(), dir, config);
 
     Document doc1 = new Document();
     doc1.add(newStringField("f1", "1", Field.Store.NO));