diff --git a/src/main/java/org/qortal/arbitrary/ArbitraryDataFile.java b/src/main/java/org/qortal/arbitrary/ArbitraryDataFile.java
index 1307eab7..2d7346ea 100644
--- a/src/main/java/org/qortal/arbitrary/ArbitraryDataFile.java
+++ b/src/main/java/org/qortal/arbitrary/ArbitraryDataFile.java
@@ -539,6 +539,50 @@ public class ArbitraryDataFile {
         return false;
     }
 
+    /**
+     * Retrieve a list of file hashes for this transaction that we do not hold locally
+     *
+     * @return a List of chunk hashes, or null if we are unable to determine what is missing
+     */
+    public List<byte[]> missingHashes() {
+        List<byte[]> missingHashes = new ArrayList<>();
+        try {
+            if (this.metadataHash == null) {
+                // We don't have any metadata so can't check if we have the chunks
+                // Even if this transaction has no chunks, we don't have the file either (already checked above)
+                return null;
+            }
+
+            if (this.metadataFile == null) {
+                this.metadataFile = ArbitraryDataFile.fromHash(this.metadataHash, this.signature);
+            }
+
+            // If the metadata file doesn't exist, we can't check if we have the chunks
+            if (!metadataFile.getFilePath().toFile().exists()) {
+                return null;
+            }
+
+            if (this.metadata == null) {
+                this.setMetadata(new ArbitraryDataTransactionMetadata(this.metadataFile.getFilePath()));
+            }
+
+            // Read the metadata
+            List<byte[]> chunks = metadata.getChunks();
+            for (byte[] chunkHash : chunks) {
+                ArbitraryDataFileChunk chunk = ArbitraryDataFileChunk.fromHash(chunkHash, this.signature);
+                if (!chunk.exists()) {
+                    missingHashes.add(chunkHash);
+                }
+            }
+
+            return missingHashes;
+
+        } catch (DataException e) {
+            // Something went wrong, so we can't make a sensible decision
+            return null;
+        }
+    }
+
     public boolean containsChunk(byte[] hash) {
         for (ArbitraryDataFileChunk chunk : this.chunks) {
             if (Arrays.equals(hash, chunk.getHash())) {
diff --git a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java
index 3147f9cb..6337fc7c 100644
--- a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java
+++ b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java
@@ -236,9 +236,11 @@ public class ArbitraryDataFileListManager {
     }
 
 
-    // Lookup file lists by signature
+    // Lookup file lists by signature (and optionally hashes)
 
     public boolean fetchArbitraryDataFileList(ArbitraryTransactionData arbitraryTransactionData) {
+        byte[] digest = arbitraryTransactionData.getData();
+        byte[] metadataHash = arbitraryTransactionData.getMetadataHash();
         byte[] signature = arbitraryTransactionData.getSignature();
         String signature58 = Base58.encode(signature);
 
@@ -261,10 +263,24 @@ public class ArbitraryDataFileListManager {
         this.addToSignatureRequests(signature58, true, false);
 
         List<Peer> handshakedPeers = Network.getInstance().getHandshakedPeers();
-        LOGGER.debug(String.format("Sending data file list request for signature %s to %d peers...", signature58, handshakedPeers.size()));
+        List<byte[]> missingHashes = null;
+
+//        // TODO: uncomment after GetArbitraryDataFileListMessage updates are deployed
+//        // Find hashes that we are missing
+//        try {
+//            ArbitraryDataFile arbitraryDataFile = ArbitraryDataFile.fromHash(digest, signature);
+//            arbitraryDataFile.setMetadataHash(metadataHash);
+//            missingHashes = arbitraryDataFile.missingHashes();
+//        } catch (DataException e) {
+//            // Leave missingHashes as null, so that all hashes are requested
+//        }
+//        int hashCount = missingHashes != null ? missingHashes.size() : 0;
+
+        int hashCount = 0;
+        LOGGER.debug(String.format("Sending data file list request for signature %s with %d hashes to %d peers...", signature58, hashCount, handshakedPeers.size()));
 
         // Build request
-        Message getArbitraryDataFileListMessage = new GetArbitraryDataFileListMessage(signature, now, 0);
+        Message getArbitraryDataFileListMessage = new GetArbitraryDataFileListMessage(signature, missingHashes, now, 0);
 
         // Save our request into requests map
         Triple<String, Peer, Long> requestEntry = new Triple<>(signature58, null, NTP.getTime());
@@ -313,12 +329,16 @@ public class ArbitraryDataFileListManager {
             return false;
         }
 
-        LOGGER.debug(String.format("Sending data file list request for signature %s to peer %s...", signature58, peer));
+        int hashCount = 0;
+        LOGGER.debug(String.format("Sending data file list request for signature %s with %d hashes to peer %s...", signature58, hashCount, peer));
 
         // Build request
         // Use a time in the past, so that the recipient peer doesn't try and relay it
+        // Also, set hashes to null since it's easier to request all hashes than it is to determine which ones we need
+        // This could be optimized in the future
         long timestamp = now - 60000L;
-        Message getArbitraryDataFileListMessage = new GetArbitraryDataFileListMessage(signature, timestamp, 0);
+        List<byte[]> hashes = null;
+        Message getArbitraryDataFileListMessage = new GetArbitraryDataFileListMessage(signature, hashes, timestamp, 0);
 
         // Save our request into requests map
         Triple<String, Peer, Long> requestEntry = new Triple<>(signature58, null, NTP.getTime());