diff --git a/src/main/java/com/github/nkzawa/engineio/client/Socket.java b/src/main/java/com/github/nkzawa/engineio/client/Socket.java
index 7ef488b..a70e94f 100644
--- a/src/main/java/com/github/nkzawa/engineio/client/Socket.java
+++ b/src/main/java/com/github/nkzawa/engineio/client/Socket.java
@@ -115,7 +115,7 @@ public class Socket extends Emitter {
     private List<String> transports;
     private List<String> upgrades;
     private Map<String, String> query;
-    private LinkedList<Packet> writeBuffer = new LinkedList<Packet>();
+    /*package*/ LinkedList<Packet> writeBuffer = new LinkedList<Packet>();
     private LinkedList<Runnable> callbackBuffer = new LinkedList<Runnable>();
     /*package*/ Transport transport;
     private Future pingTimeoutTimer;
@@ -325,6 +325,7 @@ public class Socket extends Emitter {
                             logger.fine(String.format("probe transport '%s' pong", name));
                             self.upgrading = true;
                             self.emit(EVENT_UPGRADING, transport[0]);
+                            if (null == transport) return;
                             Socket.priorWebsocketSuccess = WebSocket.NAME.equals(transport[0].name);
 
                             logger.fine(String.format("pausing current transport '%s'", self.transport.name));
@@ -332,9 +333,7 @@ public class Socket extends Emitter {
                                 @Override
                                 public void run() {
                                     if (failed[0]) return;
-                                    if (ReadyState.CLOSED == self.readyState || ReadyState.CLOSING == self.readyState) {
-                                        return;
-                                    }
+                                    if (ReadyState.CLOSED == self.readyState) return;
 
                                     logger.fine("changing transport and sending upgrade packet");
 
@@ -667,6 +666,10 @@ public class Socket extends Emitter {
     }
 
     private void sendPacket(Packet packet, Runnable fn) {
+        if (ReadyState.CLOSING == this.readyState || ReadyState.CLOSED == this.readyState) {
+            return;
+        }
+
         if (fn == null) {
             // ConcurrentLinkedList does not permit `null`.
             fn = noop;
@@ -688,11 +691,55 @@ public class Socket extends Emitter {
             @Override
             public void run() {
                 if (Socket.this.readyState == ReadyState.OPENING || Socket.this.readyState == ReadyState.OPEN) {
-                    Socket.this.onClose("forced close");
-                    logger.fine("socket closing - telling transport to close");
-                    Socket.this.transport.close();
-                }
+                    Socket.this.readyState = ReadyState.CLOSING;
 
+                    final Socket self = Socket.this;
+
+                    final Runnable close = new Runnable() {
+                        @Override
+                        public void run() {
+                            self.onClose("forced close");
+                            logger.fine("socket closing - telling transport to close");
+                            self.transport.close();
+                        }
+                    };
+
+                    final Listener[] cleanupAndClose = new Listener[1];
+                    cleanupAndClose[0] = new Listener() {
+                        @Override
+                        public void call(Object ...args) {
+                            self.off(EVENT_UPGRADE, cleanupAndClose[0]);
+                            self.off(EVENT_UPGRADE_ERROR, cleanupAndClose[0]);
+                            close.run();
+                        }
+                    };
+
+                    final Runnable waitForUpgrade = new Runnable() {
+                        @Override
+                        public void run() {
+                            // wait for updade to finish since we can't send packets while pausing a transport
+                            self.once(EVENT_UPGRADE, cleanupAndClose[0]);
+                            self.once(EVENT_UPGRADE_ERROR, cleanupAndClose[0]);
+                        }
+                    };
+
+                    if (Socket.this.writeBuffer.size() > 0) {
+                        Socket.this.once(EVENT_DRAIN, new Listener() {
+                            @Override
+                            public void call(Object... args) {
+                                if (Socket.this.upgrading) {
+                                    waitForUpgrade.run();
+                                } else {
+                                    close.run();
+                                }
+                            }
+                        });
+                    } else if (Socket.this.upgrading) {
+                        waitForUpgrade.run();
+                    } else {
+                        close.run();
+                    }
+                }
             }
         });
         return this;
@@ -710,7 +757,7 @@ public class Socket extends Emitter {
     }
 
     private void onClose(String reason, Exception desc) {
-        if (this.readyState == ReadyState.OPENING || this.readyState == ReadyState.OPEN) {
+        if (ReadyState.OPENING == this.readyState || ReadyState.OPEN == this.readyState || ReadyState.CLOSING == this.readyState) {
             logger.fine(String.format("socket close with reason: %s", reason));
             final Socket self = this;
 
diff --git a/src/test/java/com/github/nkzawa/engineio/client/ConnectionTest.java b/src/test/java/com/github/nkzawa/engineio/client/ConnectionTest.java
index 391fff1..a1f5c6a 100644
--- a/src/test/java/com/github/nkzawa/engineio/client/ConnectionTest.java
+++ b/src/test/java/com/github/nkzawa/engineio/client/ConnectionTest.java
@@ -104,6 +104,7 @@ public class ConnectionTest extends Connection {
                     }
                 });
                 socket.close();
+                socket.send("hi");
                 Timer timer = new Timer();
                 timer.schedule(new TimerTask() {
                     @Override
@@ -117,4 +118,128 @@ public class ConnectionTest extends Connection {
         socket.open();
         assertThat((Boolean)values.take(), is(true));
     }
+
+    @Test(timeout = TIMEOUT)
+    public void deferCloseWhenUpgrading() throws InterruptedException {
+        final BlockingQueue<Object> values = new LinkedBlockingQueue<Object>();
+
+        socket = new Socket(createOptions());
+        socket.on(Socket.EVENT_OPEN, new Emitter.Listener() {
+            @Override
+            public void call(Object... args) {
+                final boolean[] upgraded = new boolean[] {false};
+                socket.on(Socket.EVENT_UPGRADE, new Emitter.Listener() {
+                    @Override
+                    public void call(Object... args) {
+                        upgraded[0] = true;
+                    }
+                }).on(Socket.EVENT_UPGRADING, new Emitter.Listener() {
+                    @Override
+                    public void call(Object... args) {
+                        socket.on(Socket.EVENT_CLOSE, new Emitter.Listener() {
+                            @Override
+                            public void call(Object... args) {
+                                values.offer(upgraded[0]);
+                            }
+                        });
+                        socket.close();
+                    }
+                });
+            }
+        });
+        socket.open();
+        assertThat((Boolean)values.take(), is(true));
+    }
+
+    @Test(timeout = TIMEOUT)
+    public void closeOnUpgradeErrorIfClosingIsDeferred() throws InterruptedException {
+        final BlockingQueue<Object> values = new LinkedBlockingQueue<Object>();
+
+        socket = new Socket(createOptions());
+        socket.on(Socket.EVENT_OPEN, new Emitter.Listener() {
+            @Override
+            public void call(Object... args) {
+                final boolean[] upgradError = new boolean[] {false};
+                socket.on(Socket.EVENT_UPGRADE_ERROR, new Emitter.Listener() {
+                    @Override
+                    public void call(Object... args) {
+                        upgradError[0] = true;
+                    }
+                }).on(Socket.EVENT_UPGRADING, new Emitter.Listener() {
+                    @Override
+                    public void call(Object... args) {
+                        socket.on(Socket.EVENT_CLOSE, new Emitter.Listener() {
+                            @Override
+                            public void call(Object... args) {
+                                values.offer(upgradError[0]);
+                            }
+                        });
+                        socket.close();
+                        socket.transport.onError("upgrade error", new Exception());
+                    }
+                });
+            }
+        });
+        socket.open();
+        assertThat((Boolean) values.take(), is(true));
+    }
+
+    public void notSendPacketsIfClosingIsDeferred() throws InterruptedException {
+        final BlockingQueue<Object> values = new LinkedBlockingQueue<Object>();
+
+        socket = new Socket(createOptions());
+        socket.on(Socket.EVENT_OPEN, new Emitter.Listener() {
+            @Override
+            public void call(Object... args) {
+                final boolean[] noPacket = new boolean[] {true};
+                socket.on(Socket.EVENT_UPGRADING, new Emitter.Listener() {
+                    @Override
+                    public void call(Object... args) {
+                        socket.on(Socket.EVENT_PACKET_CREATE, new Emitter.Listener() {
+                            @Override
+                            public void call(Object... args) {
+                                noPacket[0] = false;
+                            }
+                        });
+                        socket.close();
+                        socket.send("hi");
+                    }
+                });
+                new Timer().schedule(new TimerTask() {
+                    @Override
+                    public void run() {
+                        values.offer(noPacket[0]);
+                    }
+                }, 1200);
+            }
+        });
+        socket.open();
+        assertThat((Boolean) values.take(), is(true));
+    }
+
+    @Test(timeout = TIMEOUT)
+    public void sendAllBufferedPacketsIfClosingIsDeferred() throws InterruptedException {
+        final BlockingQueue<Object> values = new LinkedBlockingQueue<Object>();
+
+        socket = new Socket(createOptions());
+        socket.on(Socket.EVENT_OPEN, new Emitter.Listener() {
+            @Override
+            public void call(Object... args) {
+                socket.on(Socket.EVENT_UPGRADING, new Emitter.Listener() {
+                    @Override
+                    public void call(Object... args) {
+                        socket.send("hi");
+                        socket.close();
+                    }
+                }).on(Socket.EVENT_CLOSE, new Emitter.Listener() {
+                    @Override
+                    public void call(Object... args) {
+                        values.offer(socket.writeBuffer.size());
+                    }
+                });
+            }
+        });
+        socket.open();
+        assertThat((Integer) values.take(), is(0));
+    }
 }