diff --git a/solr/core/src/test-files/solr/collection1/conf/solrconfig.snippet.randomindexconfig.xml b/solr/core/src/test-files/solr/collection1/conf/solrconfig.snippet.randomindexconfig.xml
index 944777515dd..0733d5c19dd 100644
--- a/solr/core/src/test-files/solr/collection1/conf/solrconfig.snippet.randomindexconfig.xml
+++ b/solr/core/src/test-files/solr/collection1/conf/solrconfig.snippet.randomindexconfig.xml
@@ -22,8 +22,11 @@ A solrconfig.xml snippet containing indexConfig settings for randomized testing.
 
 -->
 <indexConfig>
-  <!-- allways use this randomized policy -->
-  <mergePolicy class="org.apache.solr.util.RandomMergePolicy" />
+  <!-- this sys property is not set by SolrTestCaseJ4 because we ideally want to use
+       the RandomMergePolicy in all tests - but some tests expect very specific
+       Merge behavior, so those tests can set it as needed.
+  -->
+  <mergePolicy class="${solr.tests.mergePolicy:org.apache.solr.util.RandomMergePolicy}" />
   
   <useCompoundFile>${useCompoundFile:false}</useCompoundFile>
 
diff --git a/solr/core/src/test/org/apache/solr/update/DirectUpdateHandlerTest.java b/solr/core/src/test/org/apache/solr/update/DirectUpdateHandlerTest.java
index c660912ae63..77267cb01d7 100644
--- a/solr/core/src/test/org/apache/solr/update/DirectUpdateHandlerTest.java
+++ b/solr/core/src/test/org/apache/solr/update/DirectUpdateHandlerTest.java
@@ -21,6 +21,7 @@ import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 
+import org.apache.lucene.index.TieredMergePolicy;
 import org.apache.lucene.index.DirectoryReader;
 import org.apache.lucene.store.Directory;
 import org.apache.solr.SolrTestCaseJ4;
@@ -46,6 +47,7 @@ public class DirectUpdateHandlerTest extends SolrTestCaseJ4 {
     savedFactory = System.getProperty("solr.DirectoryFactory");
     System.setProperty("solr.directoryFactory", "org.apache.solr.core.MockFSDirectoryFactory");
     System.setProperty("enable.update.log", "false"); // schema12 doesn't support _version_
+    System.setProperty("solr.tests.mergePolicy", TieredMergePolicy.class.getName());
     initCore("solrconfig.xml", "schema12.xml");
   }
   
@@ -271,13 +273,14 @@ public class DirectUpdateHandlerTest extends SolrTestCaseJ4 {
     assertU(commit());
 
     assertU(adoc("id","3"));
-    assertU(adoc("id","2"));
+    assertU(adoc("id","2")); // dup, triggers delete
     assertU(adoc("id","4"));
     assertU(commit());
 
     SolrQueryRequest sr = req("q","foo");
     DirectoryReader r = sr.getSearcher().getIndexReader();
-    assertTrue(r.maxDoc() > r.numDocs());   // should have deletions
+    assertTrue("maxDoc !> numDocs ... expected some deletions",
+               r.maxDoc() > r.numDocs());
     sr.close();
 
     assertU(commit("expungeDeletes","true"));