diff --git a/dumpsearch/src/util/dump/SearchIndex.java b/dumpsearch/src/util/dump/SearchIndex.java
index a3f848e..d7a47f9 100644
--- a/dumpsearch/src/util/dump/SearchIndex.java
+++ b/dumpsearch/src/util/dump/SearchIndex.java
@@ -39,6 +39,7 @@
 import org.apache.lucene.store.AlreadyClosedException;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.FSDirectory;
+import org.apache.lucene.util.IOUtils;
 import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.Nullable;
 import org.slf4j.Logger;
@@ -109,6 +110,9 @@ public static <T> SearchIndexBuilder<T> with( @NonNull Dump<T> dump, @NonNull St
    private FacetsConfig            _facetsConfig;
    private DirectoryTaxonomyReader _taxoReader;
    private int                     _version;
+   private Directory               _writerDir;
+   private Directory               _taxoWriterDir;
+   private Directory               _taxoReaderDir;
 
    private SearchIndex( @NonNull Dump<E> dump, @NonNull FieldAccessor idFieldAccessor, @NonNull BiConsumer<Document, E> documentBuilder,
          @NonNull IndexWriterConfig config, @NonNull QueryParser queryParser, @NonNull FacetsConfig facetsConfig, int version ) {
@@ -130,18 +134,9 @@ private SearchIndex( @NonNull Dump<E> dump, @NonNull FieldAccessor idFieldAccess
    public void close() throws IOException {
       commit();
 
-      if ( _writer != null ) {
-         _writer.close();
-      }
-      if ( _taxoWriter != null ) {
-         _taxoWriter.close();
-      }
-      if ( _searcherManager != null ) {
-         _searcherManager.close();
-      }
-      if ( _taxoReader != null ) {
-         _taxoReader.close();
-      }
+      // readers must be closed before the writers they were opened on, and the Directory instances
+      // must be closed last, once nothing still has open files on them
+      IOUtils.close(_searcherManager, _taxoReader, _writer, _taxoWriter, _writerDir, _taxoWriterDir, _taxoReaderDir);
 
       super.close();
    }
@@ -379,13 +374,13 @@ protected void initLookupMap() {
    @Override
    protected void initLookupOutputStream() {
       try {
-         Directory facetDir = FSDirectory.open(new File(getLookupFile().getAbsolutePath() + "-facets").toPath());
-         _taxoWriter = new DirectoryTaxonomyWriter(facetDir);
+         _taxoWriterDir = FSDirectory.open(new File(getLookupFile().getAbsolutePath() + "-facets").toPath());
+         _taxoWriter = new DirectoryTaxonomyWriter(_taxoWriterDir);
          _taxoWriter.commit();
 
-         Directory dir = FSDirectory.open(getLookupFile().toPath());
+         _writerDir = FSDirectory.open(getLookupFile().toPath());
          _config.setOpenMode(OpenMode.CREATE_OR_APPEND);
-         _writer = new IndexWriter(dir, _config);
+         _writer = new IndexWriter(_writerDir, _config);
          _writer.commit();
 
       }
@@ -408,8 +403,8 @@ protected void openSearcher() {
       }
 
       try {
-         Directory facetDir = FSDirectory.open(new File(getLookupFile().getAbsolutePath() + "-facets").toPath());
-         _taxoReader = new DirectoryTaxonomyReader(facetDir);
+         _taxoReaderDir = FSDirectory.open(new File(getLookupFile().getAbsolutePath() + "-facets").toPath());
+         _taxoReader = new DirectoryTaxonomyReader(_taxoReaderDir);
       }
       catch ( IOException e ) {
          throw new RuntimeException("Failed to initialize dump facet index with lookup file " + getLookupFile() + "-facets", e);
diff --git a/dumpsearch/test/util/dump/SearchIndexTest.java b/dumpsearch/test/util/dump/SearchIndexTest.java
index f0f2db4..6c1d63a 100644
--- a/dumpsearch/test/util/dump/SearchIndexTest.java
+++ b/dumpsearch/test/util/dump/SearchIndexTest.java
@@ -1,6 +1,7 @@
 package util.dump;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static util.dump.SearchIndex.SortBuilder.Direction.ASC;
 import static util.dump.SearchIndex.SortBuilder.Direction.DESC;
 import static util.dump.SearchIndex.sort;
@@ -8,6 +9,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.lang.reflect.Field;
 import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -18,6 +20,8 @@
 import org.apache.lucene.document.TextField;
 import org.apache.lucene.facet.FacetField;
 import org.apache.lucene.facet.FacetResult;
+import org.apache.lucene.store.AlreadyClosedException;
+import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.BytesRef;
 import org.junit.After;
 import org.junit.Before;
@@ -165,6 +169,30 @@ public void testFaceting() throws Exception {
       }
    }
 
+   /**
+    * Regression test for the leaked {@link Directory} handles that used to keep the Lucene index directory locked
+    * and writable after {@link SearchIndex#close()} returned, which surfaced as flaky {@code DirectoryNotEmptyException}s
+    * in callers deleting the underlying folder right after close (e.g. JUnit 5's {@code @TempDir}).
+    */
+   @Test
+   public void testCloseReleasesUnderlyingLuceneDirectories() throws Exception {
+      File dumpFile = new File(_tmpdir, DUMP_FILENAME);
+      SearchIndex<Bean> index;
+
+      try (Dump<Bean> dump = new Dump<>(Bean.class, dumpFile)) {
+         index = with(dump, "_idLong", ( doc, o ) -> doc.add(new FacetField("facetField", o._data))).build();
+         dump.add(new Bean(1, "row"));
+      } // closes dump, which cascades to index.close()
+
+      for ( String fieldName : new String[]{ "_writerDir", "_taxoWriterDir", "_taxoReaderDir" } ) {
+         Field field = SearchIndex.class.getDeclaredField(fieldName);
+         field.setAccessible(true);
+         Directory dir = (Directory)field.get(index);
+         assertThat(dir).as(fieldName + " was never opened").isNotNull();
+         assertThatThrownBy(dir::listAll).as(fieldName + " was not closed by SearchIndex.close()").isInstanceOf(AlreadyClosedException.class);
+      }
+   }
+
    @Test
    public void testVersion() throws Exception {
       File dumpFile = new File(_tmpdir, DUMP_FILENAME);
diff --git a/pom.xml b/pom.xml
index b1dcd71..5772b59 100644
--- a/pom.xml
+++ b/pom.xml
@@ -23,10 +23,10 @@
       <plugins>
          <plugin>
             <artifactId>maven-compiler-plugin</artifactId>
+            <version>3.15.0</version>
             <configuration>
                <encoding>UTF-8</encoding>
-               <source>17</source>
-               <target>17</target>
+               <release>17</release>
             </configuration>
          </plugin>
          <plugin>