diff --git a/core/src/main/java/com/google/bitcoin/core/Peer.java b/core/src/main/java/com/google/bitcoin/core/Peer.java
index a3c1aff3..9b24fafb 100644
--- a/core/src/main/java/com/google/bitcoin/core/Peer.java
+++ b/core/src/main/java/com/google/bitcoin/core/Peer.java
@@ -23,10 +23,7 @@ import com.google.bitcoin.utils.EventListenerInvoker;
 import com.google.common.base.Objects;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
-import com.google.common.util.concurrent.FutureCallback;
-import com.google.common.util.concurrent.Futures;
-import com.google.common.util.concurrent.ListenableFuture;
-import com.google.common.util.concurrent.SettableFuture;
+import com.google.common.util.concurrent.*;
 import org.jboss.netty.channel.*;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -93,11 +90,15 @@ public class Peer {
     private static class GetDataRequest {
         Sha256Hash hash;
         SettableFuture future;
+        // If the peer does not support the notfound message, we'll use ping/pong messages to simulate it. This is
+        // a nasty hack that relies on the fact that bitcoin-qt is single threaded and processes messages in order.
+        // The nonce field records which pong should clear this request as "not found".
+        long nonce;
     }
-    private final List<GetDataRequest> getDataFutures;
+    private final CopyOnWriteArrayList<GetDataRequest> getDataFutures;
 
     // Outstanding pings against this peer and how long the last one took to complete.
-    private CopyOnWriteArrayList<PendingPing> pendingPings;
+    private final CopyOnWriteArrayList<PendingPing> pendingPings;
     private long[] lastPingTimes;
     private static final int PING_MOVING_AVERAGE_WINDOW = 20;
 
@@ -316,6 +317,7 @@ public class Peer {
                 if (item.hash.equals(req.hash)) {
                     req.future.cancel(true);
                     getDataFutures.remove(req);
+                    break;
                 }
             }
         }
@@ -489,11 +491,15 @@ public class Peer {
             // Build the request for the missing dependencies.
             List<ListenableFuture<Transaction>> futures = Lists.newArrayList();
             GetDataMessage getdata = new GetDataMessage(params);
+            final long nonce = (long)(Math.random()*Long.MAX_VALUE);
             for (Sha256Hash hash : needToRequest) {
                 getdata.addTransaction(hash);
                 GetDataRequest req = new GetDataRequest();
                 req.hash = hash;
                 req.future = SettableFuture.create();
+                if (!isNotFoundMessageSupported()) {
+                    req.nonce = nonce;
+                }
                 futures.add(req.future);
                 getDataFutures.add(req);
             }
@@ -538,7 +544,25 @@ public class Peer {
             });
             // Start the operation.
             sendMessage(getdata);
-        } catch (IOException e) {
+            if (!isNotFoundMessageSupported()) {
+                // If the peer isn't new enough to support the notfound message, we use a nasty hack instead and
+                // assume if we send a ping message after the getdata message, it'll be processed after all answers
+                // from getdata are done, so we can watch for the pong message as a substitute.
+                ping(nonce).addListener(new Runnable() {
+                    public void run() {
+                        // The pong came back so clear out any transactions we requested but didn't get.
+                        for (ListIterator<GetDataRequest> it = getDataFutures.listIterator(); it.hasNext();) {
+                            GetDataRequest req = it.next();
+                            if (req.nonce == nonce) {
+                                req.future.cancel(true);
+                                getDataFutures.remove(req);
+                                break;
+                            }
+                        }
+                    }
+                }, MoreExecutors.sameThreadExecutor());
+            }
+        } catch (Exception e) {
             log.error("Couldn't send getdata in downloadDependencies({})", tx.getHash());
             resultFuture.setException(e);
             return resultFuture;
@@ -973,9 +997,9 @@ public class Peer {
         // Measurement of the time elapsed.
         public long startTimeMsec;
 
-        public PendingPing() {
+        public PendingPing(long nonce) {
             future = SettableFuture.create();
-            nonce = (long) Math.random() * Long.MAX_VALUE;
+            this.nonce = nonce;
             startTimeMsec = Utils.now().getTime();
         }
 
@@ -1011,10 +1035,14 @@ public class Peer {
      * @throws ProtocolException if the peer version is too low to support measurable pings.
      */
     public synchronized ListenableFuture<Long> ping() throws IOException, ProtocolException {
+        return ping((long) Math.random() * Long.MAX_VALUE);
+    }
+
+    protected synchronized ListenableFuture<Long> ping(long nonce) throws IOException, ProtocolException {
         int peerVersion = getPeerVersionMessage().clientVersion;
         if (peerVersion < Pong.MIN_PROTOCOL_VERSION)
             throw new ProtocolException("Peer version is too low for measurable pings: " + peerVersion);
-        PendingPing pendingPing = new PendingPing();
+        PendingPing pendingPing = new PendingPing(nonce);
         pendingPings.add(pendingPing);
         sendMessage(new Ping(pendingPing.nonce));
         return pendingPing.future;
@@ -1073,6 +1101,10 @@ public class Peer {
         return chainHeight - blockChain.getBestChainHeight();
     }
 
+    private boolean isNotFoundMessageSupported() {
+        return getPeerVersionMessage().clientVersion >= 70001;
+    }
+
     /**
      * Returns true if this peer will try and download things it is sent in "inv" messages. Normally you only need
      * one peer to be downloading data. Defaults to true.
diff --git a/core/src/test/java/com/google/bitcoin/core/PeerTest.java b/core/src/test/java/com/google/bitcoin/core/PeerTest.java
index f8faa557..812ecc02 100644
--- a/core/src/test/java/com/google/bitcoin/core/PeerTest.java
+++ b/core/src/test/java/com/google/bitcoin/core/PeerTest.java
@@ -64,6 +64,7 @@ public class PeerTest extends TestWithNetworkConnections {
     private void connect(PeerHandler handler, Channel channel, ChannelHandlerContext ctx) throws Exception {
         handler.connectRequested(ctx, new UpstreamChannelStateEvent(channel, ChannelState.CONNECTED, socketAddress));
         VersionMessage peerVersion = new VersionMessage(unitTestParams, OTHER_PEER_CHAIN_HEIGHT);
+        peerVersion.clientVersion = 70001;
         DownstreamMessageEvent versionEvent = 
             new DownstreamMessageEvent(channel, Channels.future(channel), peerVersion, null);
         handler.messageReceived(ctx, versionEvent);