diff --git a/eth/downloader/downloader.go b/eth/downloader/downloader.go
index 18f8d2ba8..14ca2cd3d 100644
--- a/eth/downloader/downloader.go
+++ b/eth/downloader/downloader.go
@@ -34,6 +34,9 @@ var (
 	errPeersUnavailable    = errors.New("no peers available or all peers tried for block download process")
 	errAlreadyInPool       = errors.New("hash already in pool")
 	errBlockNumberOverflow = errors.New("received block which overflows")
+	errCancelHashFetch     = errors.New("hash fetching cancelled (requested)")
+	errCancelBlockFetch    = errors.New("block downloading cancelled (requested)")
+	errNoSyncActive        = errors.New("no sync active")
 )
 
 type hashCheckFn func(common.Hash) bool
@@ -74,6 +77,7 @@ type Downloader struct {
 	newPeerCh chan *peer
 	hashCh    chan hashPack
 	blockCh   chan blockPack
+	cancelCh  chan struct{}
 }
 
 func New(hasBlock hashCheckFn, getBlock getBlockFn) *Downloader {
@@ -129,6 +133,9 @@ func (d *Downloader) Synchronise(id string, hash common.Hash) error {
 	}
 	defer atomic.StoreInt32(&d.synchronising, 0)
 
+	// Create cancel channel for aborting midflight
+	d.cancelCh = make(chan struct{})
+
 	// Abort if the queue still contains some leftover data
 	if _, cached := d.queue.Size(); cached > 0 && d.queue.GetHeadBlock() != nil {
 		return errPendingQueue
@@ -161,7 +168,6 @@ func (d *Downloader) Has(hash common.Hash) bool {
 }
 
 func (d *Downloader) getFromPeer(p *peer, hash common.Hash, ignoreInitial bool) (err error) {
-
 	d.activePeer = p.id
 	defer func() {
 		// reset on error
@@ -191,6 +197,42 @@ func (d *Downloader) getFromPeer(p *peer, hash common.Hash, ignoreInitial bool)
 	return nil
 }
 
+// Cancel cancels all of the operations and resets the queue. It returns true
+// if the cancel operation was completed.
+func (d *Downloader) Cancel() bool {
+	hs, bs := d.queue.Size()
+	// If we're not syncing just return.
+	if atomic.LoadInt32(&d.synchronising) == 0 && hs == 0 && bs == 0 {
+		return false
+	}
+
+	close(d.cancelCh)
+
+	// clean up
+hashDone:
+	for {
+		select {
+		case <-d.hashCh:
+		default:
+			break hashDone
+		}
+	}
+
+blockDone:
+	for {
+		select {
+		case <-d.blockCh:
+		default:
+			break blockDone
+		}
+	}
+
+	// reset the queue
+	d.queue.Reset()
+
+	return true
+}
+
 // XXX Make synchronous
 func (d *Downloader) startFetchingHashes(p *peer, h common.Hash, ignoreInitial bool) error {
 	glog.V(logger.Debug).Infof("Downloading hashes (%x) from %s", h[:4], p.id)
@@ -217,6 +259,8 @@ func (d *Downloader) startFetchingHashes(p *peer, h common.Hash, ignoreInitial b
 out:
 	for {
 		select {
+		case <-d.cancelCh:
+			return errCancelHashFetch
 		case hashPack := <-d.hashCh:
 			// Make sure the active peer is giving us the hashes
 			if hashPack.peerId != activePeer.id {
@@ -305,6 +349,8 @@ func (d *Downloader) startFetchingBlocks(p *peer) error {
 out:
 	for {
 		select {
+		case <-d.cancelCh:
+			return errCancelBlockFetch
 		case blockPack := <-d.blockCh:
 			// If the peer was previously banned and failed to deliver it's pack
 			// in a reasonable time frame, ignore it's message.
@@ -394,11 +440,23 @@ out:
 
 // Deliver a chunk to the downloader. This is usually done through the BlocksMsg by
 // the protocol handler.
-func (d *Downloader) DeliverChunk(id string, blocks []*types.Block) {
+func (d *Downloader) DeliverChunk(id string, blocks []*types.Block) error {
+	// Make sure the downloader is active
+	if atomic.LoadInt32(&d.synchronising) == 0 {
+		return errNoSyncActive
+	}
+
 	d.blockCh <- blockPack{id, blocks}
+
+	return nil
 }
 
 func (d *Downloader) AddHashes(id string, hashes []common.Hash) error {
+	// Make sure the downloader is active
+	if atomic.LoadInt32(&d.synchronising) == 0 {
+		return errNoSyncActive
+	}
+
 	// make sure that the hashes that are being added are actually from the peer
 	// that's the current active peer. hashes that have been received from other
 	// peers are dropped and ignored.
diff --git a/eth/downloader/downloader_test.go b/eth/downloader/downloader_test.go
index 8ccc4d1a5..d0f8d4c8f 100644
--- a/eth/downloader/downloader_test.go
+++ b/eth/downloader/downloader_test.go
@@ -182,6 +182,49 @@ func TestTaking(t *testing.T) {
 	}
 }
 
+func TestInactiveDownloader(t *testing.T) {
+	targetBlocks := 1000
+	hashes := createHashes(0, targetBlocks)
+	blocks := createBlocksFromHashSet(createHashSet(hashes))
+	tester := newTester(t, hashes, nil)
+
+	err := tester.downloader.AddHashes("bad peer 001", hashes)
+	if err != errNoSyncActive {
+		t.Error("expected no sync error, got", err)
+	}
+
+	err = tester.downloader.DeliverChunk("bad peer 001", blocks)
+	if err != errNoSyncActive {
+		t.Error("expected no sync error, got", err)
+	}
+}
+
+func TestCancel(t *testing.T) {
+	minDesiredPeerCount = 4
+	blockTtl = 1 * time.Second
+
+	targetBlocks := 1000
+	hashes := createHashes(0, targetBlocks)
+	blocks := createBlocksFromHashes(hashes)
+	tester := newTester(t, hashes, blocks)
+
+	tester.newPeer("peer1", big.NewInt(10000), hashes[0])
+
+	err := tester.sync("peer1", hashes[0])
+	if err != nil {
+		t.Error("download error", err)
+	}
+
+	if !tester.downloader.Cancel() {
+		t.Error("cancel operation unsuccessfull")
+	}
+
+	hashSize, blockSize := tester.downloader.queue.Size()
+	if hashSize > 0 || blockSize > 0 {
+		t.Error("block (", blockSize, ") or hash (", hashSize, ") not 0")
+	}
+}
+
 func TestThrottling(t *testing.T) {
 	minDesiredPeerCount = 4
 	blockTtl = 1 * time.Second
diff --git a/eth/sync.go b/eth/sync.go
index c49f5209d..d955eaa50 100644
--- a/eth/sync.go
+++ b/eth/sync.go
@@ -63,6 +63,9 @@ func (pm *ProtocolManager) processBlocks() error {
 		max := int(math.Min(float64(len(blocks)), float64(blockProcAmount)))
 		_, err := pm.chainman.InsertChain(blocks[:max])
 		if err != nil {
+			// cancel download process
+			pm.downloader.Cancel()
+
 			return err
 		}
 		blocks = blocks[max:]