diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/T0004_PackReaderTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/T0004_PackReaderTest.java
index 67861f677..d14cc212a 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/T0004_PackReaderTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/T0004_PackReaderTest.java
@@ -46,6 +46,8 @@
 
 package org.eclipse.jgit.storage.file;
 
+import static org.eclipse.jgit.storage.pack.PackExt.INDEX;
+import static org.eclipse.jgit.storage.pack.PackExt.PACK;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 
@@ -70,7 +72,7 @@ public void test003_lookupCompressedObject() throws IOException {
 		final ObjectLoader or;
 
 		id = ObjectId.fromString("902d5476fa249b7abc9d84c611577a81381f0327");
-		pr = new PackFile(TEST_PACK);
+		pr = new PackFile(TEST_PACK, PACK.getBit() | INDEX.getBit());
 		or = pr.get(new WindowCursor(null), id);
 		assertNotNull(or);
 		assertEquals(Constants.OBJ_TREE, or.getType());
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
index 22ef45df6..7574f2aa8 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
@@ -43,6 +43,9 @@
 
 package org.eclipse.jgit.storage.file;
 
+import static org.eclipse.jgit.storage.pack.PackExt.INDEX;
+import static org.eclipse.jgit.storage.pack.PackExt.PACK;
+
 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
@@ -74,6 +77,7 @@
 import org.eclipse.jgit.lib.RepositoryCache.FileKey;
 import org.eclipse.jgit.storage.pack.CachedPack;
 import org.eclipse.jgit.storage.pack.ObjectToPack;
+import org.eclipse.jgit.storage.pack.PackExt;
 import org.eclipse.jgit.storage.pack.PackWriter;
 import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.FileUtils;
@@ -335,10 +339,23 @@ private CachedPackList scanCachedPacks(CachedPackList old)
 	public PackFile openPack(final File pack)
 			throws IOException {
 		final String p = pack.getName();
-		if (p.length() != 50 || !p.startsWith("pack-") || !p.endsWith(".pack")) //$NON-NLS-1$
+		if (p.length() != 50 || !p.startsWith("pack-") || !p.endsWith(".pack")) //$NON-NLS-1$ //$NON-NLS-2$
 			throw new IOException(MessageFormat.format(JGitText.get().notAValidPack, pack));
 
-		PackFile res = new PackFile(pack);
+		// The pack and index are assumed to exist. The existence of other
+		// extensions needs to be explicitly checked.
+		//
+		int extensions = PACK.getBit() | INDEX.getBit();
+		final String base = p.substring(0, p.length() - 4);
+		for (PackExt ext : PackExt.values()) {
+			if ((extensions & ext.getBit()) == 0) {
+				final String name = base + ext.getExtension();
+				if (new File(pack.getParentFile(), name).exists())
+					extensions |= ext.getBit();
+			}
+		}
+
+		PackFile res = new PackFile(pack, extensions);
 		insertPack(res);
 		return res;
 	}
@@ -720,9 +737,14 @@ private PackList scanPacksImpl(final PackList old) {
 			if (indexName.length() != 49 || !indexName.endsWith(".idx")) //$NON-NLS-1$
 				continue;
 
-			final String base = indexName.substring(0, indexName.length() - 4);
-			final String packName = base + ".pack"; //$NON-NLS-1$
-			if (!names.contains(packName)) {
+			final String base = indexName.substring(0, indexName.length() - 3);
+			int extensions = 0;
+			for (PackExt ext : PackExt.values()) {
+				if (names.contains(base + ext.getExtension()))
+					extensions |= ext.getBit();
+			}
+
+			if ((extensions & PACK.getBit()) == 0) {
 				// Sometimes C Git's HTTP fetch transport leaves a
 				// .idx file behind and does not download the .pack.
 				// We have to skip over such useless indexes.
@@ -730,6 +752,7 @@ private PackList scanPacksImpl(final PackList old) {
 				continue;
 			}
 
+			final String packName = base + PACK.getExtension();
 			final PackFile oldPack = forReuse.remove(packName);
 			if (oldPack != null) {
 				list.add(oldPack);
@@ -737,7 +760,7 @@ private PackList scanPacksImpl(final PackList old) {
 			}
 
 			final File packFile = new File(packDirectory, packName);
-			list.add(new PackFile(packFile));
+			list.add(new PackFile(packFile, extensions));
 			foundNew = true;
 		}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/PackFile.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/PackFile.java
index 666df58be..6c24a3fef 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/PackFile.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/PackFile.java
@@ -97,6 +97,8 @@ public int compare(final PackFile a, final PackFile b) {
 
 	private final File packFile;
 
+	private final int extensions;
+
 	private File keepFile;
 
 	private volatile String packName;
@@ -138,10 +140,13 @@ public int compare(final PackFile a, final PackFile b) {
 	 *
 	 * @param packFile
 	 *            path of the <code>.pack</code> file holding the data.
+	 * @param extensions
+	 *            additional pack file extensions with the same base as the pack
 	 */
-	public PackFile(final File packFile) {
+	public PackFile(final File packFile, int extensions) {
 		this.packFile = packFile;
 		this.packLastModified = (int) (packFile.lastModified() >> 10);
+		this.extensions = extensions;
 
 		// Multiply by 31 here so we can more directly combine with another
 		// value in WindowCache.hash(), without doing the multiply there.
@@ -1085,4 +1090,8 @@ private File extFile(PackExt ext) {
 		String b = (dot < 0) ? p : p.substring(0, dot);
 		return new File(packFile.getParentFile(), b + '.' + ext.getExtension());
 	}
+
+	private boolean hasExt(PackExt ext) {
+		return (extensions & ext.getBit()) != 0;
+	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackExt.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackExt.java
index cb33308c6..61a660930 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackExt.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackExt.java
@@ -45,21 +45,52 @@
 
 /** A pack file extension. */
 public class PackExt {
+	private static volatile PackExt[] VALUES = new PackExt[] {};
 
 	/** A pack file extension. */
-	public static final PackExt PACK = new PackExt("pack"); //$NON-NLS-1$
+	public static final PackExt PACK = newPackExt("pack"); //$NON-NLS-1$
 
 	/** A pack index file extension. */
-	public static final PackExt INDEX = new PackExt("idx"); //$NON-NLS-1$
+	public static final PackExt INDEX = newPackExt("idx"); //$NON-NLS-1$
+
+	/** @return all of the PackExt values. */
+	public static PackExt[] values() {
+		return VALUES;
+	}
+
+	/**
+	 * Returns a PackExt for the file extension and registers it in the values
+	 * array.
+	 *
+	 * @param ext
+	 *            the file extension.
+	 * @return the PackExt for the ext
+	 */
+	public synchronized static PackExt newPackExt(String ext) {
+		PackExt[] dst = new PackExt[VALUES.length + 1];
+		for (int i = 0; i < VALUES.length; i++) {
+			PackExt packExt = VALUES[i];
+			if (packExt.getExtension().equals(ext))
+				return packExt;
+			dst[i] = packExt;
+		}
+		if (VALUES.length >= 32)
+			throw new IllegalStateException(
+					"maximum number of pack extensions exceeded"); //$NON-NLS-1$
+
+		PackExt value = new PackExt(ext, VALUES.length);
+		dst[VALUES.length] = value;
+		VALUES = dst;
+		return value;
+	}
 
 	private final String ext;
 
-	/**
-	 * @param ext
-	 *            the file extension.
-	 */
-	public PackExt(String ext) {
+	private final int pos;
+
+	private PackExt(String ext, int pos) {
 		this.ext = ext;
+		this.pos = pos;
 	}
 
 	/** @return the file extension. */
@@ -67,21 +98,19 @@ public String getExtension() {
 		return ext;
 	}
 
-	@Override
-	public boolean equals(Object obj) {
-		if (obj instanceof PackExt) {
-			return ((PackExt) obj).getExtension().equals(getExtension());
-		}
-		return false;
+	/** @return the position of the extension in the values array. */
+	public int getPosition() {
+		return pos;
 	}
 
-	@Override
-	public int hashCode() {
-		return getExtension().hashCode();
+	/** @return the bit mask of the extension e.g {@code 1 << getPosition()}. */
+	public int getBit() {
+		return 1 << getPosition();
 	}
 
 	@Override
 	public String toString() {
-		return String.format("PackExt[%s]", getExtension()); //$NON-NLS-1$
+		return String.format("PackExt[%s, bit=0x%s]", getExtension(), //$NON-NLS-1$
+				Integer.toHexString(getBit()));
 	}
 }