diff --git a/core/src/test/java/org/elasticsearch/index/percolator/PercolatorQueryCacheTests.java b/core/src/test/java/org/elasticsearch/index/percolator/PercolatorQueryCacheTests.java
index 3f3d90bafbd..e10a63bca2c 100644
--- a/core/src/test/java/org/elasticsearch/index/percolator/PercolatorQueryCacheTests.java
+++ b/core/src/test/java/org/elasticsearch/index/percolator/PercolatorQueryCacheTests.java
@@ -125,6 +125,8 @@ public class PercolatorQueryCacheTests extends ESTestCase {
         IndexWriter indexWriter = new IndexWriter(
                 directory,
                 newIndexWriterConfig(new MockAnalyzer(random()))
+                        .setMergePolicy(NoMergePolicy.INSTANCE)
+                        .setMaxBufferedDocs(16)
         );
 
         boolean legacyFormat = randomBoolean();