diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteArrayWindow.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteArrayWindow.java
index 5b5a511c1..95e3e00c7 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteArrayWindow.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteArrayWindow.java
@@ -46,6 +46,7 @@
 package org.eclipse.jgit.storage.file;
 
 import java.io.IOException;
+import java.security.MessageDigest;
 import java.util.zip.CRC32;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
@@ -83,8 +84,12 @@ void crc32(CRC32 out, long pos, int cnt) {
 	}
 
 	@Override
-	void write(PackOutputStream out, long pos, int cnt) throws IOException {
-		out.write(array, (int) (pos - start), cnt);
+	void write(PackOutputStream out, long pos, int cnt, MessageDigest digest)
+			throws IOException {
+		int ptr = (int) (pos - start);
+		out.write(array, ptr, cnt);
+		if (digest != null)
+			digest.update(array, ptr, cnt);
 	}
 
 	void check(Inflater inf, byte[] tmp, long pos, int cnt)
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteBufferWindow.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteBufferWindow.java
index b9af158a0..85441589a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteBufferWindow.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteBufferWindow.java
@@ -47,6 +47,7 @@
 
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.security.MessageDigest;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
 
@@ -75,7 +76,8 @@ protected int copy(final int p, final byte[] b, final int o, int n) {
 	}
 
 	@Override
-	void write(PackOutputStream out, long pos, int cnt) throws IOException {
+	void write(PackOutputStream out, long pos, int cnt, MessageDigest digest)
+			throws IOException {
 		final ByteBuffer s = buffer.slice();
 		s.position((int) (pos - start));
 
@@ -84,6 +86,8 @@ void write(PackOutputStream out, long pos, int cnt) throws IOException {
 			int n = Math.min(cnt, buf.length);
 			s.get(buf, 0, n);
 			out.write(buf, 0, n);
+			if (digest != null)
+				digest.update(buf, 0, n);
 			cnt -= n;
 		}
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteWindow.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteWindow.java
index 3e147898b..f0b43fdb4 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteWindow.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ByteWindow.java
@@ -45,6 +45,7 @@
 package org.eclipse.jgit.storage.file;
 
 import java.io.IOException;
+import java.security.MessageDigest;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
 
@@ -120,8 +121,8 @@ final int copy(long pos, byte[] dstbuf, int dstoff, int cnt) {
 	 */
 	protected abstract int copy(int pos, byte[] dstbuf, int dstoff, int cnt);
 
-	abstract void write(PackOutputStream out, long pos, int cnt)
-			throws IOException;
+	abstract void write(PackOutputStream out, long pos, int cnt,
+			MessageDigest md) throws IOException;
 
 	final int setInput(long pos, Inflater inf) throws DataFormatException {
 		return setInput((int) (pos - start), inf);
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/LocalCachedPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/LocalCachedPack.java
index 18b32c9ea..d0461640f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/LocalCachedPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/LocalCachedPack.java
@@ -87,9 +87,10 @@ public long getObjectCount() throws IOException {
 		return cnt;
 	}
 
-	void copyAsIs(PackOutputStream out, WindowCursor wc) throws IOException {
+	void copyAsIs(PackOutputStream out, boolean validate, WindowCursor wc)
+			throws IOException {
 		for (String packName : packNames)
-			getPackFile(packName).copyPackAsIs(out, wc);
+			getPackFile(packName).copyPackAsIs(out, validate, wc);
 	}
 
 	@Override
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 80820b2ad..d8d986fb0 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
@@ -305,11 +305,11 @@ private final byte[] decompress(final long position, final int sz,
 		return dstbuf;
 	}
 
-	void copyPackAsIs(PackOutputStream out, WindowCursor curs)
+	void copyPackAsIs(PackOutputStream out, boolean validate, WindowCursor curs)
 			throws IOException {
 		// Pin the first window, this ensures the length is accurate.
 		curs.pin(this, 0);
-		curs.copyPackAsIs(this, out, 12, length - (12 + 20));
+		curs.copyPackAsIs(this, length, validate, out);
 	}
 
 	final void copyAsIs(PackOutputStream out, LocalObjectToPack src,
@@ -462,7 +462,7 @@ private void copyAsIs2(PackOutputStream out, LocalObjectToPack src,
 			// and we have it pinned.  Write this out without copying.
 			//
 			out.writeHeader(src, inflatedLength);
-			quickCopy.write(out, dataOffset, (int) dataLength);
+			quickCopy.write(out, dataOffset, (int) dataLength, null);
 
 		} else if (dataLength <= buf.length) {
 			// Tiny optimization: Lots of objects are very small deltas or
@@ -499,6 +499,10 @@ boolean invalid() {
 		return invalid;
 	}
 
+	void setInvalid() {
+		invalid = true;
+	}
+
 	private void readFully(final long position, final byte[] dstbuf,
 			int dstoff, final int cnt, final WindowCursor curs)
 			throws IOException {
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/WindowCursor.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/WindowCursor.java
index 661df62cb..e2dcae82b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/WindowCursor.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/WindowCursor.java
@@ -45,6 +45,9 @@
 package org.eclipse.jgit.storage.file;
 
 import java.io.IOException;
+import java.security.MessageDigest;
+import java.text.MessageFormat;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
@@ -52,6 +55,7 @@
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
 
+import org.eclipse.jgit.JGitText;
 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.errors.StoredObjectRepresentationNotAvailableException;
@@ -197,21 +201,52 @@ int copy(final PackFile pack, long position, final byte[] dstbuf,
 		return cnt - need;
 	}
 
-	public void copyPackAsIs(PackOutputStream out, CachedPack pack)
-			throws IOException {
-		((LocalCachedPack) pack).copyAsIs(out, this);
+	public void copyPackAsIs(PackOutputStream out, CachedPack pack,
+			boolean validate) throws IOException {
+		((LocalCachedPack) pack).copyAsIs(out, validate, this);
 	}
 
-	void copyPackAsIs(final PackFile pack, final PackOutputStream out,
-			long position, long cnt) throws IOException {
-		while (0 < cnt) {
+	void copyPackAsIs(final PackFile pack, final long length, boolean validate,
+			final PackOutputStream out) throws IOException {
+		MessageDigest md = null;
+		if (validate) {
+			md = Constants.newMessageDigest();
+			byte[] buf = out.getCopyBuffer();
+			pin(pack, 0);
+			if (window.copy(0, buf, 0, 12) != 12) {
+				pack.setInvalid();
+				throw new IOException(JGitText.get().packfileIsTruncated);
+			}
+			md.update(buf, 0, 12);
+		}
+
+		long position = 12;
+		long remaining = length - (12 + 20);
+		while (0 < remaining) {
 			pin(pack, position);
 
 			int ptr = (int) (position - window.start);
-			int n = (int) Math.min(window.size() - ptr, cnt);
-			window.write(out, position, n);
+			int n = (int) Math.min(window.size() - ptr, remaining);
+			window.write(out, position, n, md);
 			position += n;
-			cnt -= n;
+			remaining -= n;
+		}
+
+		if (md != null) {
+			byte[] buf = new byte[20];
+			byte[] actHash = md.digest();
+
+			pin(pack, position);
+			if (window.copy(position, buf, 0, 20) != 20) {
+				pack.setInvalid();
+				throw new IOException(JGitText.get().packfileIsTruncated);
+			}
+			if (!Arrays.equals(actHash, buf)) {
+				pack.setInvalid();
+				throw new IOException(MessageFormat.format(
+						JGitText.get().packfileCorruptionDetected, pack
+								.getPackFile().getPath()));
+			}
 		}
 	}
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/ObjectReuseAsIs.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/ObjectReuseAsIs.java
index 8ad0b2419..6b10349bc 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/ObjectReuseAsIs.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/ObjectReuseAsIs.java
@@ -216,9 +216,14 @@ public void copyObjectAsIs(PackOutputStream out, ObjectToPack otp,
 	 *            stream to append the pack onto.
 	 * @param pack
 	 *            the cached pack to send.
+	 * @param validate
+	 *            if true the representation must be validated and not be
+	 *            corrupt before being reused. If false, validation may be
+	 *            skipped as it will be performed elsewhere in the processing
+	 *            pipeline.
 	 * @throws IOException
 	 *             the pack cannot be read, or stream did not accept a write.
 	 */
-	public abstract void copyPackAsIs(PackOutputStream out, CachedPack pack)
-			throws IOException;
+	public abstract void copyPackAsIs(PackOutputStream out, CachedPack pack,
+			boolean validate) throws IOException;
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackWriter.java b/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackWriter.java
index 3d0604868..93c739f5b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackWriter.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/PackWriter.java
@@ -660,7 +660,7 @@ public void writePack(ProgressMonitor compressMonitor,
 			stats.reusedObjects += pack.getObjectCount();
 			stats.reusedDeltas += deltaCnt;
 			stats.totalDeltas += deltaCnt;
-			reuseSupport.copyPackAsIs(out, pack);
+			reuseSupport.copyPackAsIs(out, pack, reuseValidate);
 		}
 		writeChecksum(out);
 		out.flush();