diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/BitmapIndexImpl.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/BitmapIndexImpl.java
index 5786019e9..0f724af0d 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/BitmapIndexImpl.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/BitmapIndexImpl.java
@@ -92,6 +92,17 @@ public class BitmapIndexImpl implements BitmapIndex {
 		return new CompressedBitmap(compressed);
 	}
 
+	public CompressedBitmap toBitmap(PackBitmapIndex i,
+			EWAHCompressedBitmap b) {
+		if (i != packIndex) {
+			throw new IllegalArgumentException();
+		}
+		if (b == null) {
+			return null;
+		}
+		return new CompressedBitmap(b);
+	}
+
 	public CompressedBitmapBuilder newBitmapBuilder() {
 		return new CompressedBitmapBuilder();
 	}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java
index e244de790..ed1da4f30 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriterBitmapPreparer.java
@@ -76,6 +76,8 @@ import org.eclipse.jgit.storage.pack.PackConfig;
 import org.eclipse.jgit.util.BlockList;
 import org.eclipse.jgit.util.SystemReader;
 
+import com.googlecode.javaewah.EWAHCompressedBitmap;
+
 /**
  * Helper class for the {@link PackWriter} to select commits for which to build
  * pack index bitmaps.
@@ -347,11 +349,11 @@ class PackWriterBitmapPreparer {
 			RevCommit rc = (RevCommit) ro;
 			reuseCommits.add(new BitmapCommit(rc, false, entry.getFlags()));
 			rw.markUninteresting(rc);
-			// PackBitmapIndexRemapper.ofObjectType() ties the underlying
-			// bitmap in the old pack into the new bitmap builder.
-			bitmapRemapper.ofObjectType(bitmapRemapper.getBitmap(rc),
-					Constants.OBJ_COMMIT).trim();
-			reuse.add(rc, Constants.OBJ_COMMIT);
+			if (!reuse.contains(rc)) {
+				EWAHCompressedBitmap bitmap = bitmapRemapper.ofObjectType(
+						bitmapRemapper.getBitmap(rc), Constants.OBJ_COMMIT);
+				reuse.or(commitBitmapIndex.toBitmap(writeBitmaps, bitmap));
+			}
 		}
 
 		// Add branch tips that are not represented in old bitmap indices. Set