diff --git a/src/main/java/git/lfs/migrate/GitConverter.java b/src/main/java/git/lfs/migrate/GitConverter.java
index 537bfe5..8d08ebe 100644
--- a/src/main/java/git/lfs/migrate/GitConverter.java
+++ b/src/main/java/git/lfs/migrate/GitConverter.java
@@ -112,7 +112,7 @@ public Iterable<TaskKey> depends() throws IOException {
 
       @NotNull
       @Override
-      public ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+      public ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
         return objectId;
       }
     };
@@ -131,7 +131,7 @@ public Iterable<TaskKey> depends() {
 
       @NotNull
       @Override
-      public ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+      public ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
         final ObjectId id = resolver.resolve(TaskType.Simple, "", revObject.getObject());
         final TagBuilder builder = new TagBuilder();
         builder.setMessage(revObject.getFullMessage());
@@ -159,7 +159,7 @@ public Iterable<TaskKey> depends() {
 
       @NotNull
       @Override
-      public ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+      public ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
         final CommitBuilder builder = new CommitBuilder();
         builder.setAuthor(revObject.getAuthorIdent());
         builder.setCommitter(revObject.getCommitterIdent());
@@ -220,7 +220,7 @@ public Iterable<TaskKey> depends() throws IOException {
 
       @NotNull
       @Override
-      public ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+      public ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
         final List<GitTreeEntry> entries = getEntries();
         // Create new tree.
         Collections.sort(entries);
@@ -270,14 +270,16 @@ public Iterable<TaskKey> depends() throws IOException {
 
       @NotNull
       @Override
-      public ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+      public ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
         final ObjectLoader loader = reader.open(id, Constants.OBJ_BLOB);
         // Is empty blob (see #21)?
         if (loader.getSize() == 0) {
+          if (dstRepo.hasObject(id)) return id;
           return copy(inserter, loader);
         }
         // Is object already converted?
         if (isLfsPointer(loader)) {
+          if (dstRepo.hasObject(id)) return id;
           return copy(inserter, loader);
         }
         final String hash = (uploader == null) ? createLocalFile(id, loader) : createRemoteFile(id, loader, uploader);
@@ -388,7 +390,7 @@ public Iterable<TaskKey> depends() throws IOException {
 
       @NotNull
       @Override
-      public ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+      public ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
         final Set<String> attributes = new TreeSet<>();
         for (String glob : globs) {
           attributes.add(glob + "\tfilter=lfs diff=lfs merge=lfs -text");
@@ -423,7 +425,8 @@ public Iterable<TaskKey> depends() throws IOException {
 
       @NotNull
       @Override
-      public ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+      public ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException {
+        if (dstRepo.hasObject(id)) return id;
         return copy(inserter, reader.open(id));
       }
     };
@@ -469,7 +472,7 @@ public interface ConvertTask {
     Iterable<TaskKey> depends() throws IOException;
 
     @NotNull
-    ObjectId convert(@NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException;
+    ObjectId convert(@NotNull Repository dstRepo, @NotNull ObjectInserter inserter, @NotNull ConvertResolver resolver, @Nullable Uploader uploader) throws IOException;
   }
 
   @FunctionalInterface
diff --git a/src/main/java/git/lfs/migrate/Main.java b/src/main/java/git/lfs/migrate/Main.java
index 44bfce2..a459421 100644
--- a/src/main/java/git/lfs/migrate/Main.java
+++ b/src/main/java/git/lfs/migrate/Main.java
@@ -156,6 +156,7 @@ public static void processRepository(@NotNull Path srcPath, @NotNull Path dstPat
 
     try (DB cache = DBMaker.fileDB(cachePath.resolve("git-lfs-migrate.mapdb").toFile())
         .fileMmapEnableIfSupported()
+        .checksumHeaderBypass()
         .make()) {
       final GitConverter converter = new GitConverter(cache, dstPath, globs);
       dstRepo.create(true);
@@ -204,7 +205,7 @@ private static void processSingleThread(@NotNull GitConverter converter, @NotNul
             }
           }
           if (taskReady) {
-            final ObjectId objectId = converter.convertTask(reader, taskKey).convert(inserter, converted::get, uploader);
+            final ObjectId objectId = converter.convertTask(reader, taskKey).convert(dstRepo, inserter, converted::get, uploader);
             converted.put(taskKey, objectId);
             reporter.increment();
           }
@@ -259,7 +260,7 @@ private static Deque<TaskKey> processWithoutDependencies(@NotNull GitConverter c
               while (!done.get()) {
                 final TaskKey taskKey = channel.take();
                 if (taskKey.getType() == GitConverter.TaskType.EndMark) break;
-                final ObjectId objectId = converter.convertTask(reader, taskKey).convert(inserter, converted::get, uploader);
+                final ObjectId objectId = converter.convertTask(reader, taskKey).convert(dstRepo, inserter, converted::get, uploader);
                 converted.put(taskKey, objectId);
                 reporter.increment();
               }