diff --git a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/util/autocomplete/AstPackageExplorer.java b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/util/autocomplete/AstPackageExplorer.java
index 2d760ca884..0a85c4ad70 100644
--- a/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/util/autocomplete/AstPackageExplorer.java
+++ b/pmd-ui/src/main/java/net/sourceforge/pmd/util/fxdesigner/util/autocomplete/AstPackageExplorer.java
@@ -8,13 +8,23 @@ import java.io.File;
 import java.io.IOException;
 import java.lang.reflect.Modifier;
 import java.net.URL;
+import java.nio.file.FileVisitOption;
+import java.nio.file.FileVisitResult;
+import java.nio.file.FileVisitor;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.EnumSet;
 import java.util.Enumeration;
 import java.util.List;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import org.apache.commons.io.FilenameUtils;
+
 import net.sourceforge.pmd.lang.Language;
 
 
@@ -48,52 +58,56 @@ class AstPackageExplorer implements NodeNameFinder {
     /** Finds the classes in the given package by looking in the classpath directories. */
     private static Stream<Class<?>> getClasses(String packageName) {
 
+
         ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
         assert classLoader != null;
 
-        String path = packageName.replace('.', '/');
 
         Enumeration<URL> resources;
 
         try {
+            String path = packageName.replace('.', '/');
             resources = classLoader.getResources(path);
         } catch (IOException e) {
             return Stream.empty();
         }
 
-        List<File> dirs = new ArrayList<>();
+        final List<Class<?>> result = new ArrayList<>();
 
         while (resources.hasMoreElements()) {
             URL resource = resources.nextElement();
-            dirs.add(new File(resource.getFile()));
+            try {
+                Files.walkFileTree(new File(resource.getFile()).toPath(),
+                                   EnumSet.noneOf(FileVisitOption.class),
+                                   1,
+                                   getClassFileVisitor(packageName, result));
+
+            } catch (IOException e) {
+                // continue
+                e.printStackTrace();
+            }
         }
 
-        List<Class<?>> classes = new ArrayList<>();
-
-        for (File directory : dirs) {
-            addClasses(classes, directory, packageName);
-        }
-
-        return classes.stream();
+        return result.stream();
     }
 
 
-    private static void addClasses(List<Class<?>> classes, File directory, String packageName) {
-
-        if (!directory.exists()) {
-            return;
-        }
-
-        File[] files = directory.listFiles();
-        for (File file : files) {
-            if (file.getName().endsWith(".class")) {
-                try {
-                    classes.add(Class.forName(packageName + "." + file.getName().substring(0, file.getName().length() - ".class".length())));
-                } catch (ClassNotFoundException e) {
-                    e.printStackTrace();
+    private static FileVisitor<Path> getClassFileVisitor(String packageName, List<Class<?>> accumulator) {
+        return new SimpleFileVisitor<Path>() {
+            @Override
+            public FileVisitResult visitFile(final Path file, final BasicFileAttributes attrs) {
+                final String extension = FilenameUtils.getExtension(file.toString());
+                if ("class".equalsIgnoreCase(extension)) {
+                    try {
+                        accumulator.add(Class.forName(packageName + "." + FilenameUtils.getBaseName(file.getFileName().toString())));
+                    } catch (ClassNotFoundException e) {
+                        e.printStackTrace();
+                    }
                 }
+                return FileVisitResult.CONTINUE;
             }
-        }
+        };
+
     }