diff --git a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
index 809f9463aa6..17ea6e8c146 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestConcurrentMergeScheduler.java
@@ -154,6 +154,7 @@ public class TestConcurrentMergeScheduler extends LuceneTestCase {
     IndexWriter writer =
         new IndexWriter(
             directory, newIndexWriterConfig(new MockAnalyzer(random())).setMergePolicy(mp));
+    TestUtil.reduceOpenFiles(writer);
 
     Document doc = new Document();
     Field idField = newStringField("id", "", Field.Store.YES);
@@ -779,6 +780,7 @@ public class TestConcurrentMergeScheduler extends LuceneTestCase {
     IndexWriterConfig iwc = newIndexWriterConfig(new MockAnalyzer(random()));
     iwc.setMergePolicy(NoMergePolicy.INSTANCE);
     iwc.setMaxBufferedDocs(2);
+    iwc.setUseCompoundFile(true); // reduce open files
     IndexWriter w = new IndexWriter(dir, iwc);
     int numDocs = TEST_NIGHTLY ? 1000 : 100;
     for (int i = 0; i < numDocs; i++) {
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterThreadsToSegments.java b/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterThreadsToSegments.java
index c2d601e20d6..b4617edbc82 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterThreadsToSegments.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterThreadsToSegments.java
@@ -258,6 +258,7 @@ public class TestIndexWriterThreadsToSegments extends LuceneTestCase {
     IndexWriterConfig iwc = newIndexWriterConfig(r, new MockAnalyzer(r));
     iwc.setCommitOnClose(false);
     final RandomIndexWriter w = new RandomIndexWriter(r, dir, iwc);
+    TestUtil.reduceOpenFiles(w.w);
     w.setDoRandomForceMerge(false);
     Thread[] threads = new Thread[TestUtil.nextInt(random(), 4, 30)];
     final CountDownLatch startingGun = new CountDownLatch(1);