diff --git a/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleConnection.java b/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleConnection.java
index 5f03fc899..6e8ac40c0 100644
--- a/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleConnection.java
+++ b/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleConnection.java
@@ -270,9 +270,10 @@ public class JingleConnection implements Transferable {
         IqPacket response;
         if (returnResult) {
             response = packet.generateResponse(IqPacket.TYPE.RESULT);
-
         } else {
             response = packet.generateResponse(IqPacket.TYPE.ERROR);
+            final Element error = response.addChild("error").setAttribute("type", "cancel");
+            error.addChild("not-acceptable", "urn:ietf:params:xml:ns:xmpp-stanzas");
         }
         mXmppConnectionService.sendIqPacket(account, response, null);
     }
@@ -933,8 +934,9 @@ public class JingleConnection implements Transferable {
 
     private boolean receiveTransportAccept(JinglePacket packet) {
         if (packet.getJingleContent().hasIbbTransport()) {
-            String receivedBlockSize = packet.getJingleContent().ibbTransport()
-                    .getAttribute("block-size");
+            final Element ibbTransport = packet.getJingleContent().ibbTransport();
+            final String receivedBlockSize = ibbTransport.getAttribute("block-size");
+            final String sid = ibbTransport.getAttribute("sid");
             if (receivedBlockSize != null) {
                 try {
                     int bs = Integer.parseInt(receivedBlockSize);
@@ -947,6 +949,10 @@ public class JingleConnection implements Transferable {
             }
             this.transport = new JingleInbandTransport(this, this.transportId, this.ibbBlockSize);
 
+            if (sid == null || !sid.equals(this.transportId)) {
+                Log.w(Config.LOGTAG,String.format("%s: sid in transport-accept (%s) did not match our sid (%s) ", account.getJid().asBareJid(), sid, transportId));
+            }
+
             //might be receive instead if we are not initiating
             if (initiating()) {
                 this.transport.connect(onIbbTransportConnected);
@@ -955,6 +961,7 @@ public class JingleConnection implements Transferable {
             }
             return true;
         } else {
+            Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": received invalid transport-accept");
             return false;
         }
     }
diff --git a/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleInbandTransport.java b/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleInbandTransport.java
index 276040979..ac22614f8 100644
--- a/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleInbandTransport.java
+++ b/src/main/java/eu/siacs/conversations/xmpp/jingle/JingleInbandTransport.java
@@ -23,223 +23,217 @@ import rocks.xmpp.addr.Jid;
 
 public class JingleInbandTransport extends JingleTransport {
 
-	private Account account;
-	private Jid counterpart;
-	private int blockSize;
-	private int seq = 0;
-	private String sessionId;
+    private Account account;
+    private Jid counterpart;
+    private int blockSize;
+    private int seq = 0;
+    private String sessionId;
 
-	private boolean established = false;
+    private boolean established = false;
 
-	private boolean connected = true;
+    private boolean connected = true;
 
-	private DownloadableFile file;
-	private JingleConnection connection;
+    private DownloadableFile file;
+    private JingleConnection connection;
 
-	private InputStream fileInputStream = null;
-	private InputStream innerInputStream = null;
-	private OutputStream fileOutputStream = null;
-	private long remainingSize = 0;
-	private long fileSize = 0;
-	private MessageDigest digest;
+    private InputStream fileInputStream = null;
+    private InputStream innerInputStream = null;
+    private OutputStream fileOutputStream = null;
+    private long remainingSize = 0;
+    private long fileSize = 0;
+    private MessageDigest digest;
 
-	private OnFileTransmissionStatusChanged onFileTransmissionStatusChanged;
+    private OnFileTransmissionStatusChanged onFileTransmissionStatusChanged;
 
-	private OnIqPacketReceived onAckReceived = new OnIqPacketReceived() {
-		@Override
-		public void onIqPacketReceived(Account account, IqPacket packet) {
-			if (connected && packet.getType() == IqPacket.TYPE.RESULT) {
-				if (remainingSize > 0) {
-					sendNextBlock();
-				}
-			}
-		}
-	};
+    private OnIqPacketReceived onAckReceived = new OnIqPacketReceived() {
+        @Override
+        public void onIqPacketReceived(Account account, IqPacket packet) {
+            if (connected && packet.getType() == IqPacket.TYPE.RESULT) {
+                if (remainingSize > 0) {
+                    sendNextBlock();
+                }
+            }
+        }
+    };
 
-	public JingleInbandTransport(final JingleConnection connection, final String sid, final int blocksize) {
-		this.connection = connection;
-		this.account = connection.getAccount();
-		this.counterpart = connection.getCounterPart();
-		this.blockSize = blocksize;
-		this.sessionId = sid;
-	}
-
-	private void sendClose() {
-		IqPacket iq = new IqPacket(IqPacket.TYPE.SET);
-		iq.setTo(this.counterpart);
-		Element close = iq.addChild("close", "http://jabber.org/protocol/ibb");
-		close.setAttribute("sid", this.sessionId);
-		this.account.getXmppConnection().sendIqPacket(iq, null);
-	}
-
-	public void connect(final OnTransportConnected callback) {
-		IqPacket iq = new IqPacket(IqPacket.TYPE.SET);
-		iq.setTo(this.counterpart);
-		Element open = iq.addChild("open", "http://jabber.org/protocol/ibb");
-		open.setAttribute("sid", this.sessionId);
-		open.setAttribute("stanza", "iq");
-		open.setAttribute("block-size", Integer.toString(this.blockSize));
-		this.connected = true;
-		this.account.getXmppConnection().sendIqPacket(iq,
-				new OnIqPacketReceived() {
-
-					@Override
-					public void onIqPacketReceived(Account account,
-							IqPacket packet) {
-						if (packet.getType() != IqPacket.TYPE.RESULT) {
-							callback.failed();
-						} else {
-							callback.established();
-						}
-					}
-				});
-	}
-
-	@Override
-	public void receive(DownloadableFile file, OnFileTransmissionStatusChanged callback) {
-		this.onFileTransmissionStatusChanged = callback;
-		this.file = file;
-		try {
-			this.digest = MessageDigest.getInstance("SHA-1");
-			digest.reset();
-			this.fileOutputStream = connection.getFileOutputStream();
-			if (this.fileOutputStream == null) {
-				Log.d(Config.LOGTAG,account.getJid().asBareJid()+": could not create output stream");
-				callback.onFileTransferAborted();
-				return;
-			}
-			this.remainingSize = this.fileSize = file.getExpectedSize();
-		} catch (final NoSuchAlgorithmException | IOException e) {
-			Log.d(Config.LOGTAG,account.getJid().asBareJid()+" "+e.getMessage());
-			callback.onFileTransferAborted();
-		}
+    public JingleInbandTransport(final JingleConnection connection, final String sid, final int blocksize) {
+        this.connection = connection;
+        this.account = connection.getAccount();
+        this.counterpart = connection.getCounterPart();
+        this.blockSize = blocksize;
+        this.sessionId = sid;
     }
 
-	@Override
-	public void send(DownloadableFile file, OnFileTransmissionStatusChanged callback) {
-		this.onFileTransmissionStatusChanged = callback;
-		this.file = file;
-		try {
-			this.remainingSize = this.file.getExpectedSize();
-			this.fileSize = this.remainingSize;
-			this.digest = MessageDigest.getInstance("SHA-1");
-			this.digest.reset();
-			fileInputStream = connection.getFileInputStream();
-			if (fileInputStream == null) {
-				Log.d(Config.LOGTAG,account.getJid().asBareJid()+": could no create input stream");
-				callback.onFileTransferAborted();
-				return;
-			}
-			innerInputStream  = AbstractConnectionManager.upgrade(file, fileInputStream);
-			if (this.connected) {
-				this.sendNextBlock();
-			}
-		} catch (Exception e) {
-			callback.onFileTransferAborted();
-			Log.d(Config.LOGTAG,account.getJid().asBareJid()+": "+e.getMessage());
-		}
-	}
+    private void sendClose() {
+        IqPacket iq = new IqPacket(IqPacket.TYPE.SET);
+        iq.setTo(this.counterpart);
+        Element close = iq.addChild("close", "http://jabber.org/protocol/ibb");
+        close.setAttribute("sid", this.sessionId);
+        this.account.getXmppConnection().sendIqPacket(iq, null);
+    }
 
-	@Override
-	public void disconnect() {
-		this.connected = false;
-		FileBackend.close(fileOutputStream);
-		FileBackend.close(fileInputStream);
-	}
+    public void connect(final OnTransportConnected callback) {
+        IqPacket iq = new IqPacket(IqPacket.TYPE.SET);
+        iq.setTo(this.counterpart);
+        Element open = iq.addChild("open", "http://jabber.org/protocol/ibb");
+        open.setAttribute("sid", this.sessionId);
+        open.setAttribute("stanza", "iq");
+        open.setAttribute("block-size", Integer.toString(this.blockSize));
+        this.connected = true;
+        this.account.getXmppConnection().sendIqPacket(iq, (account, packet) -> {
+            if (packet.getType() != IqPacket.TYPE.RESULT) {
+                callback.failed();
+            } else {
+                callback.established();
+            }
+        });
+    }
 
-	private void sendNextBlock() {
-		byte[] buffer = new byte[this.blockSize];
-		try {
-			int count = innerInputStream.read(buffer);
-			if (count == -1) {
-				sendClose();
-				file.setSha1Sum(digest.digest());
-				Log.d(Config.LOGTAG,account.getJid().asBareJid()+": sendNextBlock() count was -1");
-				this.onFileTransmissionStatusChanged.onFileTransmitted(file);
-				fileInputStream.close();
-				return;
-			} else if (count != buffer.length) {
-				int rem = innerInputStream.read(buffer,count,buffer.length-count);
-				if (rem > 0) {
-					count += rem;
-				}
-			}
-			this.remainingSize -= count;
-			this.digest.update(buffer,0,count);
-			String base64 = Base64.encodeToString(buffer,0,count, Base64.NO_WRAP);
-			IqPacket iq = new IqPacket(IqPacket.TYPE.SET);
-			iq.setTo(this.counterpart);
-			Element data = iq.addChild("data", "http://jabber.org/protocol/ibb");
-			data.setAttribute("seq", Integer.toString(this.seq));
-			data.setAttribute("block-size", Integer.toString(this.blockSize));
-			data.setAttribute("sid", this.sessionId);
-			data.setContent(base64);
-			this.account.getXmppConnection().sendIqPacket(iq, this.onAckReceived);
-			this.account.getXmppConnection().r(); //don't fill up stanza queue too much
-			this.seq++;
-			connection.updateProgress((int) ((((double) (this.fileSize - this.remainingSize)) / this.fileSize) * 100));
-			if (this.remainingSize <= 0) {
-				sendClose();
-				file.setSha1Sum(digest.digest());
-				this.onFileTransmissionStatusChanged.onFileTransmitted(file);
-				fileInputStream.close();
-			}
-		} catch (IOException e) {
-			Log.d(Config.LOGTAG,account.getJid().asBareJid()+": io exception during sendNextBlock() "+e.getMessage());
-			FileBackend.close(fileInputStream);
-			this.onFileTransmissionStatusChanged.onFileTransferAborted();
-		}
-	}
+    @Override
+    public void receive(DownloadableFile file, OnFileTransmissionStatusChanged callback) {
+        this.onFileTransmissionStatusChanged = callback;
+        this.file = file;
+        try {
+            this.digest = MessageDigest.getInstance("SHA-1");
+            digest.reset();
+            this.fileOutputStream = connection.getFileOutputStream();
+            if (this.fileOutputStream == null) {
+                Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": could not create output stream");
+                callback.onFileTransferAborted();
+                return;
+            }
+            this.remainingSize = this.fileSize = file.getExpectedSize();
+        } catch (final NoSuchAlgorithmException | IOException e) {
+            Log.d(Config.LOGTAG, account.getJid().asBareJid() + " " + e.getMessage());
+            callback.onFileTransferAborted();
+        }
+    }
 
-	private void receiveNextBlock(String data) {
-		try {
-			byte[] buffer = Base64.decode(data, Base64.NO_WRAP);
-			if (this.remainingSize < buffer.length) {
-				buffer = Arrays.copyOfRange(buffer, 0, (int) this.remainingSize);
-			}
-			this.remainingSize -= buffer.length;
-			this.fileOutputStream.write(buffer);
-			this.digest.update(buffer);
-			if (this.remainingSize <= 0) {
-				file.setSha1Sum(digest.digest());
-				fileOutputStream.flush();
-				fileOutputStream.close();
-				Log.d(Config.LOGTAG,account.getJid().asBareJid()+": receive next block nothing remaining");
-				this.onFileTransmissionStatusChanged.onFileTransmitted(file);
-			} else {
-				connection.updateProgress((int) ((((double) (this.fileSize - this.remainingSize)) / this.fileSize) * 100));
-			}
-		} catch (Exception e) {
-			Log.d(Config.LOGTAG,account.getJid().asBareJid()+": "+e.getMessage());
-			FileBackend.close(fileOutputStream);
-			this.onFileTransmissionStatusChanged.onFileTransferAborted();
-		}
-	}
+    @Override
+    public void send(DownloadableFile file, OnFileTransmissionStatusChanged callback) {
+        this.onFileTransmissionStatusChanged = callback;
+        this.file = file;
+        try {
+            this.remainingSize = this.file.getExpectedSize();
+            this.fileSize = this.remainingSize;
+            this.digest = MessageDigest.getInstance("SHA-1");
+            this.digest.reset();
+            fileInputStream = connection.getFileInputStream();
+            if (fileInputStream == null) {
+                Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": could no create input stream");
+                callback.onFileTransferAborted();
+                return;
+            }
+            innerInputStream = AbstractConnectionManager.upgrade(file, fileInputStream);
+            if (this.connected) {
+                this.sendNextBlock();
+            }
+        } catch (Exception e) {
+            callback.onFileTransferAborted();
+            Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": " + e.getMessage());
+        }
+    }
 
-	public void deliverPayload(IqPacket packet, Element payload) {
-		if (payload.getName().equals("open")) {
-			if (!established) {
-				established = true;
-				connected = true;
-				this.receiveNextBlock("");
-				this.account.getXmppConnection().sendIqPacket(
-						packet.generateResponse(IqPacket.TYPE.RESULT), null);
-			} else {
-				this.account.getXmppConnection().sendIqPacket(
-						packet.generateResponse(IqPacket.TYPE.ERROR), null);
-			}
-		} else if (connected && payload.getName().equals("data")) {
-			this.receiveNextBlock(payload.getContent());
-			this.account.getXmppConnection().sendIqPacket(
-					packet.generateResponse(IqPacket.TYPE.RESULT), null);
-		} else if (connected && payload.getName().equals("close")) {
-			this.connected = false;
-			this.account.getXmppConnection().sendIqPacket(
-					packet.generateResponse(IqPacket.TYPE.RESULT), null);
-			Log.d(Config.LOGTAG,account.getJid().asBareJid()+": received ibb close");
-		} else {
-			Log.d(Config.LOGTAG,payload.toString());
-			// TODO some sort of exception
-		}
-	}
+    @Override
+    public void disconnect() {
+        this.connected = false;
+        FileBackend.close(fileOutputStream);
+        FileBackend.close(fileInputStream);
+    }
+
+    private void sendNextBlock() {
+        byte[] buffer = new byte[this.blockSize];
+        try {
+            int count = innerInputStream.read(buffer);
+            if (count == -1) {
+                sendClose();
+                file.setSha1Sum(digest.digest());
+                Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": sendNextBlock() count was -1");
+                this.onFileTransmissionStatusChanged.onFileTransmitted(file);
+                fileInputStream.close();
+                return;
+            } else if (count != buffer.length) {
+                int rem = innerInputStream.read(buffer, count, buffer.length - count);
+                if (rem > 0) {
+                    count += rem;
+                }
+            }
+            this.remainingSize -= count;
+            this.digest.update(buffer, 0, count);
+            String base64 = Base64.encodeToString(buffer, 0, count, Base64.NO_WRAP);
+            IqPacket iq = new IqPacket(IqPacket.TYPE.SET);
+            iq.setTo(this.counterpart);
+            Element data = iq.addChild("data", "http://jabber.org/protocol/ibb");
+            data.setAttribute("seq", Integer.toString(this.seq));
+            data.setAttribute("block-size", Integer.toString(this.blockSize));
+            data.setAttribute("sid", this.sessionId);
+            data.setContent(base64);
+            this.account.getXmppConnection().sendIqPacket(iq, this.onAckReceived);
+            this.account.getXmppConnection().r(); //don't fill up stanza queue too much
+            this.seq++;
+            connection.updateProgress((int) ((((double) (this.fileSize - this.remainingSize)) / this.fileSize) * 100));
+            if (this.remainingSize <= 0) {
+                sendClose();
+                file.setSha1Sum(digest.digest());
+                this.onFileTransmissionStatusChanged.onFileTransmitted(file);
+                fileInputStream.close();
+            }
+        } catch (IOException e) {
+            Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": io exception during sendNextBlock() " + e.getMessage());
+            FileBackend.close(fileInputStream);
+            this.onFileTransmissionStatusChanged.onFileTransferAborted();
+        }
+    }
+
+    private void receiveNextBlock(String data) {
+        try {
+            byte[] buffer = Base64.decode(data, Base64.NO_WRAP);
+            if (this.remainingSize < buffer.length) {
+                buffer = Arrays.copyOfRange(buffer, 0, (int) this.remainingSize);
+            }
+            this.remainingSize -= buffer.length;
+            this.fileOutputStream.write(buffer);
+            this.digest.update(buffer);
+            if (this.remainingSize <= 0) {
+                file.setSha1Sum(digest.digest());
+                fileOutputStream.flush();
+                fileOutputStream.close();
+                Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": receive next block nothing remaining");
+                this.onFileTransmissionStatusChanged.onFileTransmitted(file);
+            } else {
+                connection.updateProgress((int) ((((double) (this.fileSize - this.remainingSize)) / this.fileSize) * 100));
+            }
+        } catch (Exception e) {
+            Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": " + e.getMessage());
+            FileBackend.close(fileOutputStream);
+            this.onFileTransmissionStatusChanged.onFileTransferAborted();
+        }
+    }
+
+    public void deliverPayload(IqPacket packet, Element payload) {
+        if (payload.getName().equals("open")) {
+            if (!established) {
+                established = true;
+                connected = true;
+                this.receiveNextBlock("");
+                this.account.getXmppConnection().sendIqPacket(
+                        packet.generateResponse(IqPacket.TYPE.RESULT), null);
+            } else {
+                this.account.getXmppConnection().sendIqPacket(
+                        packet.generateResponse(IqPacket.TYPE.ERROR), null);
+            }
+        } else if (connected && payload.getName().equals("data")) {
+            this.receiveNextBlock(payload.getContent());
+            this.account.getXmppConnection().sendIqPacket(
+                    packet.generateResponse(IqPacket.TYPE.RESULT), null);
+        } else if (connected && payload.getName().equals("close")) {
+            this.connected = false;
+            this.account.getXmppConnection().sendIqPacket(
+                    packet.generateResponse(IqPacket.TYPE.RESULT), null);
+            Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": received ibb close");
+        } else {
+            Log.d(Config.LOGTAG, payload.toString());
+            // TODO some sort of exception
+        }
+    }
 }