diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/IndexPackTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/IndexPackTest.java
index 110804f91..6015428d9 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/IndexPackTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/IndexPackTest.java
@@ -58,6 +58,7 @@ import org.eclipse.jgit.junit.TestRepository;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.NullProgressMonitor;
 import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.RepositoryTestCase;
 import org.eclipse.jgit.lib.TextProgressMonitor;
 import org.eclipse.jgit.revwalk.RevBlob;
@@ -151,6 +152,25 @@ public class IndexPackTest extends RepositoryTestCase {
 		ip.renameAndOpenPack();
 	}
 
+	public void testPackWithDuplicateBlob() throws Exception {
+		final byte[] data = Constants.encode("0123456789abcdefg");
+		TestRepository<Repository> d = new TestRepository<Repository>(db);
+		assertTrue(db.hasObject(d.blob(data)));
+
+		TemporaryBuffer.Heap pack = new TemporaryBuffer.Heap(1024);
+		packHeader(pack, 1);
+		pack.write((Constants.OBJ_BLOB) << 4 | 0x80 | 1);
+		pack.write(1);
+		deflate(pack, data);
+		digest(pack);
+
+		final byte[] raw = pack.toByteArray();
+		IndexPack ip = IndexPack.create(db, new ByteArrayInputStream(raw));
+		ip.setStreamFileThreshold(1);
+		ip.index(NullProgressMonitor.INSTANCE);
+		ip.renameAndOpenPack();
+	}
+
 	private void packHeader(TemporaryBuffer.Heap tinyPack, int cnt)
 			throws IOException {
 		final byte[] hdr = new byte[8];
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/IndexPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/IndexPack.java
index d7d1373c8..8feb483fe 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/IndexPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/IndexPack.java
@@ -75,6 +75,7 @@ import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectIdSubclassMap;
 import org.eclipse.jgit.lib.ObjectLoader;
 import org.eclipse.jgit.lib.ObjectReader;
+import org.eclipse.jgit.lib.ObjectStream;
 import org.eclipse.jgit.lib.ProgressMonitor;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.storage.file.PackIndexWriter;
@@ -144,6 +145,8 @@ public class IndexPack {
 
 	private final Repository repo;
 
+	private int streamFileThreshold;
+
 	/**
 	 * Object database used for loading existing objects
 	 */
@@ -151,6 +154,8 @@ public class IndexPack {
 
 	private InflaterStream inflater;
 
+	private byte[] readBuffer;
+
 	private final MessageDigest objectDigest;
 
 	private final MutableObjectId tempObjectId;
@@ -211,6 +216,9 @@ public class IndexPack {
 
 	private LongMap<UnresolvedDelta> baseByPos;
 
+	/** Blobs whose contents need to be double-checked after indexing. */
+	private List<PackedObjectInfo> deferredCheckBlobs;
+
 	private MessageDigest packDigest;
 
 	private RandomAccessFile packOut;
@@ -236,11 +244,13 @@ public class IndexPack {
 	public IndexPack(final Repository db, final InputStream src,
 			final File dstBase) throws IOException {
 		repo = db;
+		streamFileThreshold = 5 * (1 << 20); // A reasonable default for now.
 		objectDatabase = db.getObjectDatabase().newCachedDatabase();
 		in = src;
 		inflater = new InflaterStream();
 		readCurs = objectDatabase.newReader();
 		buf = new byte[BUFFER_SIZE];
+		readBuffer = new byte[BUFFER_SIZE];
 		objectDigest = Constants.newMessageDigest();
 		tempObjectId = new MutableObjectId();
 		packDigest = Constants.newMessageDigest();
@@ -258,6 +268,10 @@ public class IndexPack {
 		}
 	}
 
+	void setStreamFileThreshold(int sz) {
+		streamFileThreshold = sz;
+	}
+
 	/**
 	 * Set the pack index file format version this instance will create.
 	 *
@@ -396,6 +410,7 @@ public class IndexPack {
 				entries = new PackedObjectInfo[(int) objectCount];
 				baseById = new ObjectIdSubclassMap<DeltaChain>();
 				baseByPos = new LongMap<UnresolvedDelta>();
+				deferredCheckBlobs = new ArrayList<PackedObjectInfo>();
 
 				progress.beginTask(JGitText.get().receivingObjects,
 						(int) objectCount);
@@ -407,6 +422,8 @@ public class IndexPack {
 				}
 				readPackFooter();
 				endInput();
+				if (!deferredCheckBlobs.isEmpty())
+					doDeferredCheckBlobs();
 				progress.endTask();
 				if (deltaCount > 0) {
 					if (packOut == null)
@@ -837,17 +854,38 @@ public class IndexPack {
 
 	private void whole(final int type, final long pos, final long sz)
 			throws IOException {
-		final byte[] data = inflateAndReturn(Source.INPUT, sz);
 		objectDigest.update(Constants.encodedTypeString(type));
 		objectDigest.update((byte) ' ');
 		objectDigest.update(Constants.encodeASCII(sz));
 		objectDigest.update((byte) 0);
-		objectDigest.update(data);
-		tempObjectId.fromRaw(objectDigest.digest(), 0);
 
-		verifySafeObject(tempObjectId, type, data);
+		boolean checkContentLater = false;
+		if (type == Constants.OBJ_BLOB && sz >= streamFileThreshold) {
+			InputStream inf = inflate(Source.INPUT, sz);
+			long cnt = 0;
+			while (cnt < sz) {
+				int r = inf.read(readBuffer);
+				if (r <= 0)
+					break;
+				objectDigest.update(readBuffer, 0, r);
+				cnt += r;
+			}
+			inf.close();
+			tempObjectId.fromRaw(objectDigest.digest(), 0);
+			checkContentLater = readCurs.has(tempObjectId);
+
+		} else {
+			final byte[] data = inflateAndReturn(Source.INPUT, sz);
+			objectDigest.update(data);
+			tempObjectId.fromRaw(objectDigest.digest(), 0);
+			verifySafeObject(tempObjectId, type, data);
+		}
+
 		final int crc32 = (int) crc.getValue();
-		addObjectAndTrack(new PackedObjectInfo(pos, crc32, tempObjectId));
+		PackedObjectInfo obj = new PackedObjectInfo(pos, crc32, tempObjectId);
+		addObjectAndTrack(obj);
+		if (checkContentLater)
+			deferredCheckBlobs.add(obj);
 	}
 
 	private void verifySafeObject(final AnyObjectId id, final int type,
@@ -863,7 +901,7 @@ public class IndexPack {
 
 		try {
 			final ObjectLoader ldr = readCurs.open(id, type);
-			final byte[] existingData = ldr.getCachedBytes(Integer.MAX_VALUE);
+			final byte[] existingData = ldr.getCachedBytes(data.length);
 			if (!Arrays.equals(data, existingData)) {
 				throw new IOException(MessageFormat.format(JGitText.get().collisionOn, id.name()));
 			}
@@ -874,6 +912,49 @@ public class IndexPack {
 		}
 	}
 
+	private void doDeferredCheckBlobs() throws IOException {
+		final byte[] curBuffer = new byte[readBuffer.length];
+		for (PackedObjectInfo obj : deferredCheckBlobs) {
+			position(obj.getOffset());
+
+			int c = readFrom(Source.FILE);
+			final int type = (c >> 4) & 7;
+			long sz = c & 15;
+			int shift = 4;
+			while ((c & 0x80) != 0) {
+				c = readFrom(Source.FILE);
+				sz += (c & 0x7f) << shift;
+				shift += 7;
+			}
+
+			if (type != Constants.OBJ_BLOB)
+				throw new IOException(MessageFormat.format(
+						JGitText.get().unknownObjectType, type));
+
+			ObjectStream cur = readCurs.open(obj, type).openStream();
+			try {
+				if (cur.getSize() != sz)
+					throw new IOException(MessageFormat.format(
+							JGitText.get().collisionOn, obj.name()));
+				InputStream pck = inflate(Source.FILE, sz);
+				while (0 < sz) {
+					int n = (int) Math.min(readBuffer.length, sz);
+					IO.readFully(cur, curBuffer, 0, n);
+					IO.readFully(pck, readBuffer, 0, n);
+					for (int i = 0; i < n; i++) {
+						if (curBuffer[i] != readBuffer[i])
+							throw new IOException(MessageFormat.format(JGitText
+									.get().collisionOn, obj.name()));
+					}
+					sz -= n;
+				}
+				pck.close();
+			} finally {
+				cur.close();
+			}
+		}
+	}
+
 	// Current position of {@link #bOffset} within the entire file.
 	private long position() {
 		return bBase + bOffset;