diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsInserterTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsInserterTest.java
index a54c81be4..b84a0b00a 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsInserterTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsInserterTest.java
@@ -10,6 +10,8 @@
 
 package org.eclipse.jgit.internal.storage.dfs;
 
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_MIN_BYTES_OBJ_SIZE_INDEX;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_PACK_SECTION;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertSame;
@@ -289,6 +291,27 @@ public void testObjectSizePopulated() throws IOException {
 		}
 	}
 
+	@Test
+	public void testObjectSizeIndexOnInsert() throws IOException {
+		db.getConfig().setInt(CONFIG_PACK_SECTION, null,
+				CONFIG_KEY_MIN_BYTES_OBJ_SIZE_INDEX, 0);
+
+		byte[] contents = Constants.encode("foo");
+		ObjectId fooId;
+		try (ObjectInserter ins = db.newObjectInserter()) {
+			fooId = ins.insert(Constants.OBJ_BLOB, contents);
+			ins.flush();
+		}
+
+		DfsReader reader = db.getObjectDatabase().newReader();
+		assertEquals(1, db.getObjectDatabase().listPacks().size());
+		DfsPackFile insertPack = db.getObjectDatabase().getPacks()[0];
+		assertEquals(PackSource.INSERT,
+				insertPack.getPackDescription().getPackSource());
+		assertTrue(insertPack.hasObjectSizeIndex(reader));
+		assertEquals(contents.length, insertPack.getIndexedObjectSize(reader, fooId));
+	}
+
 	private static String readString(ObjectLoader loader) throws IOException {
 		return RawParseUtils.decode(readStream(loader));
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java
index 5f25905a5..2f8d964e0 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java
@@ -11,6 +11,7 @@
 package org.eclipse.jgit.internal.storage.dfs;
 
 import static org.eclipse.jgit.internal.storage.pack.PackExt.INDEX;
+import static org.eclipse.jgit.internal.storage.pack.PackExt.OBJECT_SIZE_INDEX;
 import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
 import static org.eclipse.jgit.lib.Constants.OBJ_OFS_DELTA;
 import static org.eclipse.jgit.lib.Constants.OBJ_REF_DELTA;
@@ -42,6 +43,7 @@
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.file.PackIndex;
 import org.eclipse.jgit.internal.storage.file.PackIndexWriter;
+import org.eclipse.jgit.internal.storage.file.PackObjectSizeIndexWriter;
 import org.eclipse.jgit.internal.storage.pack.PackExt;
 import org.eclipse.jgit.lib.AbbreviatedObjectId;
 import org.eclipse.jgit.lib.AnyObjectId;
@@ -52,6 +54,7 @@
 import org.eclipse.jgit.lib.ObjectLoader;
 import org.eclipse.jgit.lib.ObjectReader;
 import org.eclipse.jgit.lib.ObjectStream;
+import org.eclipse.jgit.storage.pack.PackConfig;
 import org.eclipse.jgit.transport.PackedObjectInfo;
 import org.eclipse.jgit.util.BlockList;
 import org.eclipse.jgit.util.IO;
@@ -192,6 +195,11 @@ public void flush() throws IOException {
 		sortObjectsById();
 
 		PackIndex index = writePackIndex(packDsc, packHash, objectList);
+		PackConfig pConfig = new PackConfig(db.getRepository().getConfig());
+		if (pConfig.isWriteObjSizeIndex()) {
+			writeObjectSizeIndex(packDsc, objectList,
+					pConfig.getMinBytesForObjSizeIndex());
+		}
 		db.commitPack(Collections.singletonList(packDsc), null);
 		rollback = false;
 
@@ -314,6 +322,18 @@ private static void index(OutputStream out, byte[] packHash,
 		PackIndexWriter.createVersion(out, INDEX_VERSION).write(list, packHash);
 	}
 
+	void writeObjectSizeIndex(DfsPackDescription pack,
+			List<PackedObjectInfo> packedObjs, int minSize) throws IOException {
+		try (DfsOutputStream os = db.writeFile(pack, PackExt.OBJECT_SIZE_INDEX);
+				CountingOutputStream cnt = new CountingOutputStream(os)) {
+			PackObjectSizeIndexWriter.createWriter(os, minSize)
+					.write(packedObjs);
+			pack.addFileExt(OBJECT_SIZE_INDEX);
+			pack.setBlockSize(OBJECT_SIZE_INDEX, os.blockSize());
+			pack.setFileSize(OBJECT_SIZE_INDEX, cnt.getCount());
+		}
+	}
+
 	private class PackStream extends OutputStream {
 		private final DfsOutputStream out;
 		private final MessageDigest md;