diff --git a/core/src/main/java/org/jboss/jandex/Index.java b/core/src/main/java/org/jboss/jandex/Index.java
index 3c4fc75c..b652e15e 100644
--- a/core/src/main/java/org/jboss/jandex/Index.java
+++ b/core/src/main/java/org/jboss/jandex/Index.java
@@ -22,16 +22,20 @@
 import java.io.FileFilter;
 import java.io.FileInputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Enumeration;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
 
 /**
  * An index useful for quickly processing annotations. The index is read-only and supports
@@ -137,30 +141,50 @@ public static Index of(Class<?>... classes) throws IOException {
     }
 
     /**
-     * Constructs an Index of class files found in the passed directories.
-     * The directories are <i>not</i> scanned recursively.
+     * Constructs an Index of the passed files and directories. Files may be class files or JAR files.
+     * Directories are scanned for class files, but <i>not</i> recursively.
      *
-     * @param directories Directories containing class files to index
+     * @param files class files, JAR files or directories containing class files to index
      * @return the index
-     * @throws IllegalArgumentException if any passed {@code File} is null or not a directory
+     * @throws IllegalArgumentException if any passed {@code File} is null or not a class file, JAR file or directory
      */
-    public static Index of(File... directories) throws IOException {
+    public static Index of(File... files) throws IOException {
         Indexer indexer = new Indexer();
 
-        for (File directory : directories) {
-            if (directory == null || !directory.isDirectory()) {
-                throw new IllegalArgumentException("not a directory: " + directory);
-            }
+        for (File file : files) {
+            if (file == null) {
+                throw new IllegalArgumentException("File must not be null");
+            } else if (file.isDirectory()) {
+                File[] classFiles = file.listFiles(new FileFilter() {
+                    @Override
+                    public boolean accept(File pathname) {
+                        return pathname.isFile() && pathname.getName().endsWith(".class");
+                    }
+                });
 
-            File[] sources = directory.listFiles(new FileFilter() {
-                @Override
-                public boolean accept(File pathname) {
-                    return pathname.isFile() && pathname.getName().endsWith(".class");
+                for (File classFile : classFiles) {
+                    try (InputStream in = new FileInputStream(classFile)) {
+                        indexer.index(in);
+                    }
                 }
-            });
-
-            for (File source : sources) {
-                indexer.index(new FileInputStream(source));
+            } else if (file.isFile() && file.getName().endsWith(".class")) {
+                try (InputStream in = new FileInputStream(file)) {
+                    indexer.index(in);
+                }
+            } else if (file.isFile() && file.getName().endsWith(".jar")) {
+                try (JarFile jarFile = new JarFile(file)) {
+                    Enumeration<JarEntry> entries = jarFile.entries();
+                    while (entries.hasMoreElements()) {
+                        JarEntry entry = entries.nextElement();
+                        if (entry.getName().endsWith(".class")) {
+                            try (InputStream in = jarFile.getInputStream(entry)) {
+                                indexer.index(in);
+                            }
+                        }
+                    }
+                }
+            } else {
+                throw new IllegalArgumentException("Not a class file, JAR file or directory: " + file);
             }
         }
 
diff --git a/core/src/main/java/org/jboss/jandex/Indexer.java b/core/src/main/java/org/jboss/jandex/Indexer.java
index b5e9d64a..7a661b11 100644
--- a/core/src/main/java/org/jboss/jandex/Indexer.java
+++ b/core/src/main/java/org/jboss/jandex/Indexer.java
@@ -2030,8 +2030,9 @@ public ClassInfo indexClass(Class<?> clazz) throws IOException {
             throw new IllegalArgumentException("clazz cannot be null");
         }
         String resourceName = '/' + clazz.getName().replace('.', '/') + ".class";
-        InputStream resource = clazz.getResourceAsStream(resourceName);
-        return index(resource);
+        try (InputStream resource = clazz.getResourceAsStream(resourceName)) {
+            return index(resource);
+        }
     }
 
     /**
@@ -2054,7 +2055,7 @@ public ClassInfo index(InputStream stream) throws IOException {
 
             // Retroweaved classes may contain annotations
             // Also, hierarchy info is needed regardless
-            if (!isJDK11OrNewer(data))
+            if (!isJDK11OrNewer(data)) // refers to JDK 1.1, not JDK 11
                 return null;
 
             initIndexMaps();
diff --git a/core/src/test/java/org/jboss/jandex/test/BasicTestCase.java b/core/src/test/java/org/jboss/jandex/test/BasicTestCase.java
index f5b75197..35fac03d 100644
--- a/core/src/test/java/org/jboss/jandex/test/BasicTestCase.java
+++ b/core/src/test/java/org/jboss/jandex/test/BasicTestCase.java
@@ -277,10 +277,19 @@ public boolean accept(File pathname) {
 
     @Test
     public void testIndexOfEmptyDirectory() throws IOException, URISyntaxException {
-        URL testLocation = getClass().getResource(getClass().getSimpleName() + ".class");
-        File testDirectory = new File(testLocation.toURI().resolve("../../../../"));
-        Index index = Index.of(testDirectory);
-        assertEquals(0, index.getKnownClasses().size());
+        File tempDir = null;
+
+        try {
+            tempDir = File.createTempFile("temp", ".dir");
+            tempDir.delete();
+            tempDir.mkdir();
+            Index index = Index.of(tempDir);
+            assertEquals(0, index.getKnownClasses().size());
+        } finally {
+            if (tempDir != null) {
+                tempDir.delete();
+            }
+        }
     }
 
     @Test
@@ -306,19 +315,43 @@ public void testIndexOfDirectoryNonClassFile() throws IOException, URISyntaxExce
     }
 
     @Test
-    public void testIndexOfNonDirectory() throws IOException, URISyntaxException {
+    public void testIndexOfClassFile() throws IOException, URISyntaxException {
         final URL testLocation = getClass().getResource(getClass().getSimpleName() + ".class");
         final File thisClassFile = new File(testLocation.toURI());
-        assertThrows(IllegalArgumentException.class, new ThrowingRunnable() {
-            @Override
-            public void run() throws Throwable {
-                Index.of(thisClassFile);
+        Index index = Index.of(thisClassFile);
+        assertEquals(1, index.getKnownClasses().size());
+    }
+
+    @Test
+    public void testIndexOfNonClassFile() throws IOException {
+        File tempDir = null;
+        File tempFile = null;
+
+        try {
+            tempDir = File.createTempFile("temp", ".dir");
+            tempDir.delete();
+            tempDir.mkdir();
+            tempFile = File.createTempFile("dummy", ".tmp", tempDir);
+
+            File temp = tempFile;
+            assertThrows(IllegalArgumentException.class, new ThrowingRunnable() {
+                @Override
+                public void run() throws Throwable {
+                    Index.of(temp);
+                }
+            });
+        } finally {
+            if (tempFile != null) {
+                tempFile.delete();
             }
-        });
+            if (tempDir != null) {
+                tempDir.delete();
+            }
+        }
     }
 
     @Test
-    public void testIndexOfNullDirectory() throws IOException, URISyntaxException {
+    public void testIndexOfNullDirectory() {
         assertThrows(IllegalArgumentException.class, new ThrowingRunnable() {
             @Override
             public void run() throws Throwable {