diff --git a/serial/rfc2217.py b/serial/rfc2217.py
index d388038..2ae188e 100644
--- a/serial/rfc2217.py
+++ b/serial/rfc2217.py
@@ -76,7 +76,7 @@
 
 import serial
 from serial.serialutil import SerialBase, SerialException, to_bytes, \
-    iterbytes, portNotOpenError, Timeout
+    iterbytes, PortNotOpenError, Timeout
 
 # port string is expected to be something like this:
 # rfc2217://host:port
@@ -598,7 +598,7 @@
     def in_waiting(self):
         """Return the number of bytes currently in the input buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return self._read_buffer.qsize()
 
     def read(self, size=1):
@@ -608,7 +608,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         data = bytearray()
         try:
             timeout = Timeout(self._timeout)
@@ -632,7 +632,7 @@
         closed.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         with self._write_lock:
             try:
                 self._socket.sendall(to_bytes(data).replace(IAC, IAC_DOUBLED))
@@ -643,7 +643,7 @@
     def reset_input_buffer(self):
         """Clear input buffer, discarding all that is in the buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.rfc2217_send_purge(PURGE_RECEIVE_BUFFER)
         # empty read buffer
         while self._read_buffer.qsize():
@@ -655,7 +655,7 @@
         discarding all that is in the buffer.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.rfc2217_send_purge(PURGE_TRANSMIT_BUFFER)
 
     def _update_break_state(self):
@@ -664,7 +664,7 @@
         possible.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('set BREAK to {}'.format('active' if self._break_state else 'inactive'))
         if self._break_state:
@@ -675,7 +675,7 @@
     def _update_rts_state(self):
         """Set terminal status line: Request To Send."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('set RTS to {}'.format('active' if self._rts_state else 'inactive'))
         if self._rts_state:
@@ -686,7 +686,7 @@
     def _update_dtr_state(self):
         """Set terminal status line: Data Terminal Ready."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('set DTR to {}'.format('active' if self._dtr_state else 'inactive'))
         if self._dtr_state:
@@ -698,28 +698,28 @@
     def cts(self):
         """Read terminal status line: Clear To Send."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return bool(self.get_modem_state() & MODEMSTATE_MASK_CTS)
 
     @property
     def dsr(self):
         """Read terminal status line: Data Set Ready."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return bool(self.get_modem_state() & MODEMSTATE_MASK_DSR)
 
     @property
     def ri(self):
         """Read terminal status line: Ring Indicator."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return bool(self.get_modem_state() & MODEMSTATE_MASK_RI)
 
     @property
     def cd(self):
         """Read terminal status line: Carrier Detect."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return bool(self.get_modem_state() & MODEMSTATE_MASK_CD)
 
     # - - - platform specific - - -
diff --git a/serial/serialcli.py b/serial/serialcli.py
index ddd0cdf..4614736 100644
--- a/serial/serialcli.py
+++ b/serial/serialcli.py
@@ -148,7 +148,7 @@
     def in_waiting(self):
         """Return the number of characters currently in the input buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return self._port_handle.BytesToRead
 
     def read(self, size=1):
@@ -158,7 +158,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         # must use single byte reads as this is the only way to read
         # without applying encodings
         data = bytearray()
@@ -174,7 +174,7 @@
     def write(self, data):
         """Output the given string over the serial port."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         #~ if not isinstance(data, (bytes, bytearray)):
             #~ raise TypeError('expected %s or bytearray, got %s' % (bytes, type(data)))
         try:
@@ -182,13 +182,13 @@
             # as this is the only one not applying encodings
             self._port_handle.Write(as_byte_array(data), 0, len(data))
         except System.TimeoutException:
-            raise writeTimeoutError
+            raise SerialTimeoutException('Write timeout')
         return len(data)
 
     def reset_input_buffer(self):
         """Clear input buffer, discarding all that is in the buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._port_handle.DiscardInBuffer()
 
     def reset_output_buffer(self):
@@ -197,7 +197,7 @@
         discarding all that is in the buffer.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._port_handle.DiscardOutBuffer()
 
     def _update_break_state(self):
@@ -205,40 +205,40 @@
         Set break: Controls TXD. When active, to transmitting is possible.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._port_handle.BreakState = bool(self._break_state)
 
     def _update_rts_state(self):
         """Set terminal status line: Request To Send"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._port_handle.RtsEnable = bool(self._rts_state)
 
     def _update_dtr_state(self):
         """Set terminal status line: Data Terminal Ready"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._port_handle.DtrEnable = bool(self._dtr_state)
 
     @property
     def cts(self):
         """Read terminal status line: Clear To Send"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return self._port_handle.CtsHolding
 
     @property
     def dsr(self):
         """Read terminal status line: Data Set Ready"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return self._port_handle.DsrHolding
 
     @property
     def ri(self):
         """Read terminal status line: Ring Indicator"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         #~ return self._port_handle.XXX
         return False  # XXX an error would be better
 
@@ -246,7 +246,7 @@
     def cd(self):
         """Read terminal status line: Carrier Detect"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return self._port_handle.CDHolding
 
     # - - platform specific - - - -
diff --git a/serial/serialjava.py b/serial/serialjava.py
index 9c920c5..0789a78 100644
--- a/serial/serialjava.py
+++ b/serial/serialjava.py
@@ -152,7 +152,7 @@
     def in_waiting(self):
         """Return the number of characters currently in the input buffer."""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return self._instream.available()
 
     def read(self, size=1):
@@ -162,7 +162,7 @@
         until the requested number of bytes is read.
         """
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         read = bytearray()
         if size > 0:
             while len(read) < size:
@@ -177,7 +177,7 @@
     def write(self, data):
         """Output the given string over the serial port."""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if not isinstance(data, (bytes, bytearray)):
             raise TypeError('expected %s or bytearray, got %s' % (bytes, type(data)))
         self._outstream.write(data)
@@ -186,7 +186,7 @@
     def reset_input_buffer(self):
         """Clear input buffer, discarding all that is in the buffer."""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._instream.skip(self._instream.available())
 
     def reset_output_buffer(self):
@@ -195,57 +195,57 @@
         discarding all that is in the buffer.
         """
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._outstream.flush()
 
     def send_break(self, duration=0.25):
         """Send break condition. Timed, returns to idle state after given duration."""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.sPort.sendBreak(duration*1000.0)
 
     def _update_break_state(self):
         """Set break: Controls TXD. When active, to transmitting is possible."""
         if self.fd is None:
-            raise portNotOpenError
+            raise PortNotOpenError()
         raise SerialException("The _update_break_state function is not implemented in java.")
 
     def _update_rts_state(self):
         """Set terminal status line: Request To Send"""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.sPort.setRTS(self._rts_state)
 
     def _update_dtr_state(self):
         """Set terminal status line: Data Terminal Ready"""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.sPort.setDTR(self._dtr_state)
 
     @property
     def cts(self):
         """Read terminal status line: Clear To Send"""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.sPort.isCTS()
 
     @property
     def dsr(self):
         """Read terminal status line: Data Set Ready"""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.sPort.isDSR()
 
     @property
     def ri(self):
         """Read terminal status line: Ring Indicator"""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.sPort.isRI()
 
     @property
     def cd(self):
         """Read terminal status line: Carrier Detect"""
         if not self.sPort:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.sPort.isCD()
diff --git a/serial/serialposix.py b/serial/serialposix.py
index 334ba9f..f31b99d 100644
--- a/serial/serialposix.py
+++ b/serial/serialposix.py
@@ -39,7 +39,7 @@
 
 import serial
 from serial.serialutil import SerialBase, SerialException, to_bytes, \
-    portNotOpenError, writeTimeoutError, Timeout
+    PortNotOpenError, SerialTimeoutException, Timeout
 
 
 class PlatformSpecificBase(object):
@@ -532,7 +532,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         read = bytearray()
         timeout = Timeout(self._timeout)
         while len(read) < size:
@@ -585,7 +585,7 @@
     def write(self, data):
         """Output the given byte string over the serial port."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         d = to_bytes(data)
         tx_len = length = len(d)
         timeout = Timeout(self._write_timeout)
@@ -600,13 +600,13 @@
                     # when timeout is set, use select to wait for being ready
                     # with the time left as timeout
                     if timeout.expired():
-                        raise writeTimeoutError
+                        raise SerialTimeoutException('Write timeout')
                     abort, ready, _ = select.select([self.pipe_abort_write_r], [self.fd], [], timeout.time_left())
                     if abort:
                         os.read(self.pipe_abort_write_r, 1000)
                         break
                     if not ready:
-                        raise writeTimeoutError
+                        raise SerialTimeoutException('Write timeout')
                 else:
                     assert timeout.time_left() is None
                     # wait for write operation
@@ -633,7 +633,7 @@
                 if e[0] not in (errno.EAGAIN, errno.EALREADY, errno.EWOULDBLOCK, errno.EINPROGRESS, errno.EINTR):
                     raise SerialException('write failed: {}'.format(e))
             if not timeout.is_non_blocking and timeout.expired():
-                raise writeTimeoutError
+                raise SerialTimeoutException('Write timeout')
         return length - len(d)
 
     def flush(self):
@@ -642,13 +642,13 @@
         is written.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         termios.tcdrain(self.fd)
 
     def reset_input_buffer(self):
         """Clear input buffer, discarding all that is in the buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         termios.tcflush(self.fd, termios.TCIFLUSH)
 
     def reset_output_buffer(self):
@@ -657,7 +657,7 @@
         that is in the buffer.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         termios.tcflush(self.fd, termios.TCOFLUSH)
 
     def send_break(self, duration=0.25):
@@ -666,7 +666,7 @@
         duration.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         termios.tcsendbreak(self.fd, int(duration / 0.25))
 
     def _update_rts_state(self):
@@ -687,7 +687,7 @@
     def cts(self):
         """Read terminal status line: Clear To Send"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         s = fcntl.ioctl(self.fd, TIOCMGET, TIOCM_zero_str)
         return struct.unpack('I', s)[0] & TIOCM_CTS != 0
 
@@ -695,7 +695,7 @@
     def dsr(self):
         """Read terminal status line: Data Set Ready"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         s = fcntl.ioctl(self.fd, TIOCMGET, TIOCM_zero_str)
         return struct.unpack('I', s)[0] & TIOCM_DSR != 0
 
@@ -703,7 +703,7 @@
     def ri(self):
         """Read terminal status line: Ring Indicator"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         s = fcntl.ioctl(self.fd, TIOCMGET, TIOCM_zero_str)
         return struct.unpack('I', s)[0] & TIOCM_RI != 0
 
@@ -711,7 +711,7 @@
     def cd(self):
         """Read terminal status line: Carrier Detect"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         s = fcntl.ioctl(self.fd, TIOCMGET, TIOCM_zero_str)
         return struct.unpack('I', s)[0] & TIOCM_CD != 0
 
@@ -730,7 +730,7 @@
         WARNING: this function is not portable to different platforms!
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         return self.fd
 
     def set_input_flow_control(self, enable=True):
@@ -740,7 +740,7 @@
         WARNING: this function is not portable to different platforms!
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if enable:
             termios.tcflow(self.fd, termios.TCION)
         else:
@@ -753,7 +753,7 @@
         WARNING: this function is not portable to different platforms!
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if enable:
             termios.tcflow(self.fd, termios.TCOON)
         else:
@@ -779,7 +779,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         read = bytearray()
         timeout = Timeout(self._timeout)
         poll = select.poll()
@@ -856,7 +856,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         read = bytearray()
         while len(read) < size:
             buf = os.read(self.fd, size - len(read))
diff --git a/serial/serialutil.py b/serial/serialutil.py
index 2785b6f..8c5ccfe 100644
--- a/serial/serialutil.py
+++ b/serial/serialutil.py
@@ -97,8 +97,10 @@
     """Write timeouts give an exception"""
 
 
-writeTimeoutError = SerialTimeoutException('Write timeout')
-portNotOpenError = SerialException('Attempting to use a port that is not open')
+class PortNotOpenError(SerialException):
+    """Port is not open"""
+    def __init__(self):
+        super(PortNotOpenError, self).__init__('Attempting to use a port that is not open')
 
 
 class Timeout(object):
@@ -574,7 +576,7 @@
         duration.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self.break_condition = True
         time.sleep(duration)
         self.break_condition = False
diff --git a/serial/serialwin32.py b/serial/serialwin32.py
index bd1944c..54d3e12 100644
--- a/serial/serialwin32.py
+++ b/serial/serialwin32.py
@@ -17,7 +17,7 @@
 from serial import win32
 
 import serial
-from serial.serialutil import SerialBase, SerialException, to_bytes, portNotOpenError, writeTimeoutError
+from serial.serialutil import SerialBase, SerialException, to_bytes, PortNotOpenError, SerialTimeoutException
 
 
 class Serial(SerialBase):
@@ -266,7 +266,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if size > 0:
             win32.ResetEvent(self._overlapped_read.hEvent)
             flags = win32.DWORD()
@@ -303,7 +303,7 @@
     def write(self, data):
         """Output the given byte string over the serial port."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         #~ if not isinstance(data, (bytes, bytearray)):
             #~ raise TypeError('expected %s or bytearray, got %s' % (bytes, type(data)))
         # convert data (needed in case of memoryview instance: Py 3.1 io lib), ctypes doesn't like memoryview
@@ -322,7 +322,7 @@
                 if win32.GetLastError() == win32.ERROR_OPERATION_ABORTED:
                     return n.value  # canceled IO is no error
                 if n.value != len(data):
-                    raise writeTimeoutError
+                    raise SerialTimeoutException('Write timeout')
                 return n.value
             else:
                 errorcode = win32.ERROR_SUCCESS if success else win32.GetLastError()
@@ -351,7 +351,7 @@
     def reset_input_buffer(self):
         """Clear input buffer, discarding all that is in the buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         win32.PurgeComm(self._port_handle, win32.PURGE_RXCLEAR | win32.PURGE_RXABORT)
 
     def reset_output_buffer(self):
@@ -360,13 +360,13 @@
         that is in the buffer.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         win32.PurgeComm(self._port_handle, win32.PURGE_TXCLEAR | win32.PURGE_TXABORT)
 
     def _update_break_state(self):
         """Set break: Controls TXD. When active, to transmitting is possible."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self._break_state:
             win32.SetCommBreak(self._port_handle)
         else:
@@ -388,7 +388,7 @@
 
     def _GetCommModemStatus(self):
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         stat = win32.DWORD()
         win32.GetCommModemStatus(self._port_handle, ctypes.byref(stat))
         return stat.value
@@ -432,7 +432,7 @@
         WARNING: this function is not portable to different platforms!
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if enable:
             win32.EscapeCommFunction(self._port_handle, win32.SETXON)
         else:
diff --git a/serial/urlhandler/protocol_cp2110.py b/serial/urlhandler/protocol_cp2110.py
index 04ba03e..44ad4eb 100644
--- a/serial/urlhandler/protocol_cp2110.py
+++ b/serial/urlhandler/protocol_cp2110.py
@@ -40,7 +40,7 @@
 import hid  # hidapi
 
 import serial
-from serial.serialutil import SerialBase, SerialException, portNotOpenError, to_bytes, Timeout
+from serial.serialutil import SerialBase, SerialException, PortNotOpenError, to_bytes, Timeout
 
 
 # Report IDs and related constant
@@ -185,7 +185,7 @@
 
     def reset_input_buffer(self):
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._hid_handle.send_feature_report(
             bytes((_REPORT_SET_PURGE_FIFOS, _PURGE_RX_FIFO)))
         # empty read buffer
@@ -194,13 +194,13 @@
 
     def reset_output_buffer(self):
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         self._hid_handle.send_feature_report(
             bytes((_REPORT_SET_PURGE_FIFOS, _PURGE_TX_FIFO)))
 
     def _update_break_state(self):
         if not self._hid_handle:
-            raise portNotOpenError
+            raise PortNotOpenError()
 
         if self._break_state:
             self._hid_handle.send_feature_report(
@@ -214,7 +214,7 @@
 
     def read(self, size=1):
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
 
         data = bytearray()
         try:
@@ -234,7 +234,7 @@
 
     def write(self, data):
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         data = to_bytes(data)
         tx_len = len(data)
         while tx_len > 0:
diff --git a/serial/urlhandler/protocol_loop.py b/serial/urlhandler/protocol_loop.py
index 985e7a7..526583f 100644
--- a/serial/urlhandler/protocol_loop.py
+++ b/serial/urlhandler/protocol_loop.py
@@ -27,7 +27,7 @@
 except ImportError:
     import Queue as queue
 
-from serial.serialutil import SerialBase, SerialException, to_bytes, iterbytes, writeTimeoutError, portNotOpenError
+from serial.serialutil import SerialBase, SerialException, to_bytes, iterbytes, SerialTimeoutException, PortNotOpenError
 
 # map log level names to constants. used in from_url()
 LOGGER_LEVELS = {
@@ -127,7 +127,7 @@
     def in_waiting(self):
         """Return the number of bytes currently in the input buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             # attention the logged value can differ from return value in
             # threaded environments...
@@ -141,7 +141,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self._timeout is not None and self._timeout != 0:
             timeout = time.time() + self._timeout
         else:
@@ -181,7 +181,7 @@
         """
         self._cancel_write = False
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         data = to_bytes(data)
         # calculate aprox time that would be used to send the data
         time_used_to_send = 10.0 * len(data) / self._baudrate
@@ -195,7 +195,7 @@
                 time_left -= 0.5
             if self._cancel_write:
                 return 0  # XXX
-            raise writeTimeoutError
+            raise SerialTimeoutException('Write timeout')
         for byte in iterbytes(data):
             self.queue.put(byte, timeout=self._write_timeout)
         return len(data)
@@ -203,7 +203,7 @@
     def reset_input_buffer(self):
         """Clear input buffer, discarding all that is in the buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('reset_input_buffer()')
         try:
@@ -218,7 +218,7 @@
         discarding all that is in the buffer.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('reset_output_buffer()')
         try:
@@ -249,7 +249,7 @@
     def cts(self):
         """Read terminal status line: Clear To Send"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('CTS -> state of RTS ({!r})'.format(self._rts_state))
         return self._rts_state
@@ -265,7 +265,7 @@
     def ri(self):
         """Read terminal status line: Ring Indicator"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for RI')
         return False
@@ -274,7 +274,7 @@
     def cd(self):
         """Read terminal status line: Carrier Detect"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for CD')
         return True
diff --git a/serial/urlhandler/protocol_socket.py b/serial/urlhandler/protocol_socket.py
index 11f6a05..2888467 100644
--- a/serial/urlhandler/protocol_socket.py
+++ b/serial/urlhandler/protocol_socket.py
@@ -29,7 +29,7 @@
     import urllib.parse as urlparse
 
 from serial.serialutil import SerialBase, SerialException, to_bytes, \
-    portNotOpenError, writeTimeoutError, Timeout
+    PortNotOpenError, SerialTimeoutException, Timeout
 
 # map log level names to constants. used in from_url()
 LOGGER_LEVELS = {
@@ -136,7 +136,7 @@
     def in_waiting(self):
         """Return the number of bytes currently in the input buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         # Poll the socket to see if it is ready for reading.
         # If ready, at least one byte will be to read.
         lr, lw, lx = select.select([self._socket], [], [], 0)
@@ -152,7 +152,7 @@
         until the requested number of bytes is read.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         read = bytearray()
         timeout = Timeout(self._timeout)
         while len(read) < size:
@@ -193,7 +193,7 @@
         closed.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
 
         d = to_bytes(data)
         tx_len = length = len(d)
@@ -209,10 +209,10 @@
                     # when timeout is set, use select to wait for being ready
                     # with the time left as timeout
                     if timeout.expired():
-                        raise writeTimeoutError
+                        raise SerialTimeoutException('Write timeout')
                     _, ready, _ = select.select([], [self._socket], [], timeout.time_left())
                     if not ready:
-                        raise writeTimeoutError
+                        raise SerialTimeoutException('Write timeout')
                 else:
                     assert timeout.time_left() is None
                     # wait for write operation
@@ -236,13 +236,13 @@
                 if e[0] not in (errno.EAGAIN, errno.EALREADY, errno.EWOULDBLOCK, errno.EINPROGRESS, errno.EINTR):
                     raise SerialException('write failed: {}'.format(e))
             if not timeout.is_non_blocking and timeout.expired():
-                raise writeTimeoutError
+                raise SerialTimeoutException('Write timeout')
         return length - len(d)
 
     def reset_input_buffer(self):
         """Clear input buffer, discarding all that is in the buffer."""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
 
         # just use recv to remove input, while there is some
         ready = True
@@ -270,7 +270,7 @@
         discarding all that is in the buffer.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored reset_output_buffer')
 
@@ -280,7 +280,7 @@
         duration.
         """
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored send_break({!r})'.format(duration))
 
@@ -304,7 +304,7 @@
     def cts(self):
         """Read terminal status line: Clear To Send"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for cts')
         return True
@@ -313,7 +313,7 @@
     def dsr(self):
         """Read terminal status line: Data Set Ready"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for dsr')
         return True
@@ -322,7 +322,7 @@
     def ri(self):
         """Read terminal status line: Ring Indicator"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for ri')
         return False
@@ -331,7 +331,7 @@
     def cd(self):
         """Read terminal status line: Carrier Detect"""
         if not self.is_open:
-            raise portNotOpenError
+            raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for cd)')
         return True
diff --git a/test/handlers/protocol_test.py b/test/handlers/protocol_test.py
index f2e572f..c0cffa6 100644
--- a/test/handlers/protocol_test.py
+++ b/test/handlers/protocol_test.py
@@ -80,7 +80,7 @@
 
     def inWaiting(self):
         """Return the number of characters currently in the input buffer."""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             # set this one to debug as the function could be called often...
             self.logger.debug('WARNING: inWaiting returns dummy value')
@@ -90,7 +90,7 @@
         """Read size bytes from the serial port. If a timeout is set it may
         return less characters as requested. With no timeout it will block
         until the requested number of bytes is read."""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         data = '123' # dummy data
         return bytes(data)
 
@@ -98,73 +98,73 @@
         """Output the given string over the serial port. Can block if the
         connection is blocked. May raise SerialException if the connection is
         closed."""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         # nothing done
         return len(data)
 
     def flushInput(self):
         """Clear input buffer, discarding all that is in the buffer."""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored flushInput')
 
     def flushOutput(self):
         """Clear output buffer, aborting the current output and
         discarding all that is in the buffer."""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored flushOutput')
 
     def sendBreak(self, duration=0.25):
         """Send break condition. Timed, returns to idle state after given
         duration."""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored sendBreak({!r})'.format(duration))
 
     def setBreak(self, level=True):
         """Set break: Controls TXD. When active, to transmitting is
         possible."""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored setBreak({!r})'.format(level))
 
     def setRTS(self, level=True):
         """Set terminal status line: Request To Send"""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored setRTS({!r})'.format(level))
 
     def setDTR(self, level=True):
         """Set terminal status line: Data Terminal Ready"""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('ignored setDTR({!r})'.format(level))
 
     def getCTS(self):
         """Read terminal status line: Clear To Send"""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for getCTS()')
         return True
 
     def getDSR(self):
         """Read terminal status line: Data Set Ready"""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for getDSR()')
         return True
 
     def getRI(self):
         """Read terminal status line: Ring Indicator"""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for getRI()')
         return False
 
     def getCD(self):
         """Read terminal status line: Carrier Detect"""
-        if not self._isOpen: raise portNotOpenError
+        if not self._isOpen: raise PortNotOpenError()
         if self.logger:
             self.logger.info('returning dummy for getCD()')
         return True