diff --git a/lucene/core/src/test/org/apache/lucene/index/TestNRTThreads.java b/lucene/core/src/test/org/apache/lucene/index/TestNRTThreads.java
index 9490bfe8325..ab6ffa1101e 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestNRTThreads.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestNRTThreads.java
@@ -54,7 +54,7 @@ public class TestNRTThreads extends ThreadedIndexingAndSearchingTestCase {
         }
         r.close();
         writer.commit();
-        final Set<String> openDeletedFiles = ((MockDirectoryWrapper) dir).getOpenDeletedFiles();
+        final Set<String> openDeletedFiles = dir.getOpenDeletedFiles();
         if (openDeletedFiles.size() > 0) {
           System.out.println("OBD files: " + openDeletedFiles);
         }
@@ -80,7 +80,7 @@ public class TestNRTThreads extends ThreadedIndexingAndSearchingTestCase {
     r.close();
 
     //System.out.println("numDocs=" + r.numDocs() + " openDelFileCount=" + dir.openDeleteFileCount());
-    final Set<String> openDeletedFiles = ((MockDirectoryWrapper) dir).getOpenDeletedFiles();
+    final Set<String> openDeletedFiles = dir.getOpenDeletedFiles();
     if (openDeletedFiles.size() > 0) {
       System.out.println("OBD files: " + openDeletedFiles);
     }
diff --git a/lucene/test-framework/src/java/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java b/lucene/test-framework/src/java/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java
index e8d7dcaa1da..370d0b4384b 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java
@@ -37,8 +37,8 @@ import org.apache.lucene.search.Sort;
 import org.apache.lucene.search.SortField;
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.TopDocs;
-import org.apache.lucene.store.BaseDirectoryWrapper;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.MockDirectoryWrapper;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.FailOnNonBulkMergesInfoStream;
@@ -60,7 +60,7 @@ public abstract class ThreadedIndexingAndSearchingTestCase extends LuceneTestCas
   protected final AtomicInteger delCount = new AtomicInteger();
   protected final AtomicInteger packCount = new AtomicInteger();
 
-  protected Directory dir;
+  protected MockDirectoryWrapper dir;
   protected IndexWriter writer;
 
   private static class SubDocs {
@@ -432,8 +432,8 @@ public abstract class ThreadedIndexingAndSearchingTestCase extends LuceneTestCas
     Random random = new Random(random().nextLong());
     final LineFileDocs docs = new LineFileDocs(random, true);
     final File tempDir = _TestUtil.getTempDir(testName);
-    dir = newFSDirectory(tempDir);
-    ((BaseDirectoryWrapper) dir).setCheckIndexOnClose(false); // don't double-checkIndex, we do it ourselves.
+    dir = newMockFSDirectory(tempDir); // some subclasses rely on this being MDW
+    dir.setCheckIndexOnClose(false); // don't double-checkIndex, we do it ourselves.
     final IndexWriterConfig conf = newIndexWriterConfig(TEST_VERSION_CURRENT, 
         new MockAnalyzer(random())).setInfoStream(new FailOnNonBulkMergesInfoStream());
 
diff --git a/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java b/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
index a656dafd74f..d26b9d47457 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
@@ -806,6 +806,10 @@ public abstract class LuceneTestCase extends Assert {
     return (MockDirectoryWrapper) wrapDirectory(r, newDirectoryImpl(r, TEST_DIRECTORY), false);
   }
 
+  public static MockDirectoryWrapper newMockFSDirectory(File f) {
+    return (MockDirectoryWrapper) newFSDirectory(f, null, false);
+  }
+
   /**
    * Returns a new Directory instance, with contents copied from the
    * provided directory. See {@link #newDirectory()} for more
@@ -822,6 +826,10 @@ public abstract class LuceneTestCase extends Assert {
 
   /** Returns a new FSDirectory instance over the given file, which must be a folder. */
   public static BaseDirectoryWrapper newFSDirectory(File f, LockFactory lf) {
+    return newFSDirectory(f, lf, rarely());
+  }
+
+  private static BaseDirectoryWrapper newFSDirectory(File f, LockFactory lf, boolean bare) {
     String fsdirClass = TEST_DIRECTORY;
     if (fsdirClass.equals("random")) {
       fsdirClass = RandomPicks.randomFrom(random(), FS_DIRECTORIES); 
@@ -838,7 +846,7 @@ public abstract class LuceneTestCase extends Assert {
       }
 
       Directory fsdir = newFSDirectoryImpl(clazz, f);
-      BaseDirectoryWrapper wrapped = wrapDirectory(random(), fsdir, rarely());
+      BaseDirectoryWrapper wrapped = wrapDirectory(random(), fsdir, bare);
       if (lf != null) {
         wrapped.setLockFactory(lf);
       }