diff --git a/src/net/packetsocket.cpp b/src/net/packetsocket.cpp
index 7095b28f2907f647e85ec211e562ace4b763313c..80c7a67b57e9c3de0c1c31f6b3a312407ce5f90f 100644
--- a/src/net/packetsocket.cpp
+++ b/src/net/packetsocket.cpp
@@ -15,6 +15,7 @@ namespace net
 PacketSocket::PacketSocket(SocketDevice *sock)
     : TrafficShapedSocket(sock)
     , ctrl_packets_sent(0)
+    , pending_upload_data_bytes(0)
     , uploaded_data_bytes(0)
 {
 }
@@ -22,6 +23,7 @@ PacketSocket::PacketSocket(SocketDevice *sock)
 PacketSocket::PacketSocket(int fd, int ip_version)
     : TrafficShapedSocket(fd, ip_version)
     , ctrl_packets_sent(0)
+    , pending_upload_data_bytes(0)
     , uploaded_data_bytes(0)
 {
 }
@@ -29,6 +31,7 @@ PacketSocket::PacketSocket(int fd, int ip_version)
 PacketSocket::PacketSocket(bool tcp, int ip_version)
     : TrafficShapedSocket(tcp, ip_version)
     , ctrl_packets_sent(0)
+    , pending_upload_data_bytes(0)
     , uploaded_data_bytes(0)
 {
 }
@@ -82,6 +85,7 @@ Uint32 PacketSocket::write(Uint32 max, bt::TimeStamp now)
             QMutexLocker locker(&mutex);
             if (curr_packet->getType() == PIECE) {
                 up_speed->onData(ret, now);
+                pending_upload_data_bytes -= ret;
                 uploaded_data_bytes += ret;
             }
         } else
@@ -113,10 +117,12 @@ Uint32 PacketSocket::write(Uint32 max, bt::TimeStamp now)
 
 void PacketSocket::addPacket(Packet::Ptr packet)
 {
+    Q_ASSERT(!packet->sending());
     QMutexLocker locker(&mutex);
-    if (packet->getType() == PIECE)
+    if (packet->getType() == PIECE) {
         data_packets.push_back(packet);
-    else
+        pending_upload_data_bytes += packet->getDataLength();
+    } else
         control_packets.push_back(packet);
     // tell upload thread we have data ready should it be sleeping
     net::SocketMonitor::instance().signalPacketReady();
@@ -151,7 +157,7 @@ void PacketSocket::clearPieces(bool reject)
         if (p->getType() == bt::PIECE && !p->sending() && curr_packet != p) {
             if (reject)
                 addPacket(Packet::Ptr(p->makeRejectOfPiece()));
-
+            pending_upload_data_bytes -= p->getDataLength();
             i = data_packets.erase(i);
         } else {
             i++;
@@ -166,6 +172,7 @@ void PacketSocket::doNotSendPiece(const bt::Request &req, bool reject)
     while (i != data_packets.end()) {
         Packet::Ptr p = *i;
         if (p->isPiece(req) && !p->sending() && p != curr_packet) {
+            pending_upload_data_bytes -= p->getDataLength();
             i = data_packets.erase(i);
             if (reject) {
                 // queue a reject packet
@@ -183,4 +190,10 @@ Uint32 PacketSocket::numPendingPieceUploads() const
     return data_packets.size();
 }
 
+Uint32 PacketSocket::numPendingPieceUploadBytes() const
+{
+    QMutexLocker locker(&mutex);
+    return pending_upload_data_bytes;
+}
+
 }
diff --git a/src/net/packetsocket.h b/src/net/packetsocket.h
index bbcb9e5e476d69b3b0bf341dc830663b9e1c9e45..8d06bbc5f4cf202fb8a09c7867f38f75ed5f4768 100644
--- a/src/net/packetsocket.h
+++ b/src/net/packetsocket.h
@@ -61,6 +61,9 @@ public:
     /// Get the number of pending piece uploads
     Uint32 numPendingPieceUploads() const;
 
+    /// Get the number of pending piece upload bytes (including message headers)
+    Uint32 numPendingPieceUploadBytes() const;
+
 protected:
     /**
      * Preprocess the packet data, before it is sent. Default implementation does nothing.
@@ -77,6 +80,7 @@ protected:
     bt::Packet::Ptr curr_packet;
     Uint32 ctrl_packets_sent;
 
+    Uint32 pending_upload_data_bytes;
     Uint32 uploaded_data_bytes;
 };
 
diff --git a/src/peer/peer.cpp b/src/peer/peer.cpp
index 0f0fffda3ef755b1a654f6823cc18c0e6eff1ff0..09a7b9d923f2c7125b332318242397d85d636244 100644
--- a/src/peer/peer.cpp
+++ b/src/peer/peer.cpp
@@ -32,6 +32,8 @@ using namespace net;
 namespace bt
 {
 static const int MAX_METADATA_SIZE = 100 * 1024 * 1024; // maximum allowed metadata_size (up to 100 MiB)
+static const unsigned MAX_PENDING_UPLOAD_BLOCKS = 512; // allow up to 8 MiB of 16KiB blocks
+static const Uint32 MAX_PENDING_UPLOAD_BYTES = MAX_PENDING_UPLOAD_BLOCKS * (13 + 16384);
 static Uint32 peer_id_counter = 1;
 bool Peer::resolve_hostname = true;
 
@@ -818,6 +820,12 @@ bool Peer::sendChunk(Uint32 index, Uint32 begin, Uint32 len, Chunk *ch)
         Out(SYS_CON | LOG_NOTICE) << "\tPiece : begin = " << begin << " len = " << len << endl;
         return false;
     }
+    if (sock->numPendingPieceUploads() >= MAX_PENDING_UPLOAD_BLOCKS ||
+        sock->numPendingPieceUploadBytes() + 13 + len > MAX_PENDING_UPLOAD_BYTES)
+    {
+        Out(SYS_CON | LOG_NOTICE) << "Warning : rejecting piece request due to limit on pending uploads" << endl;
+        return false;
+    }
     /*      Out(SYS_CON|LOG_DEBUG) << QString("Uploading %1 %2 %3 %4 %5")
      *          .arg(index).arg(begin).arg(len).arg((quint64)ch,0,16).arg((quint64)ch->getData(),0,16)
      *          << endl;;