diff --git a/lucene/src/test/org/apache/lucene/index/TestIndexWriterReader.java b/lucene/src/test/org/apache/lucene/index/TestIndexWriterReader.java
index c987aafedc6..7cc33ccf631 100644
--- a/lucene/src/test/org/apache/lucene/index/TestIndexWriterReader.java
+++ b/lucene/src/test/org/apache/lucene/index/TestIndexWriterReader.java
@@ -128,6 +128,9 @@ public class TestIndexWriterReader extends LuceneTestCase {
 
     Directory dir1 = newDirectory();
     IndexWriter writer = new IndexWriter(dir1, newIndexWriterConfig( TEST_VERSION_CURRENT, new MockAnalyzer()));
+    // test relies on no merges happening below:
+    ((LogMergePolicy) writer.getMergePolicy()).setMergeFactor(10);
+
     writer.setInfoStream(infoStream);
     // create the index
     createIndexNoClose(!optimize, "index1", writer);