diff --git a/nut2.py b/nut2.py
index 872dfd4..44aa35f 100644
--- a/nut2.py
+++ b/nut2.py
@@ -73,7 +73,7 @@ def __del__(self):
         # Try to disconnect cleanly when class is deleted.
         if self._srv_handler:
             try:
-                self._srv_handler.write("LOGOUT\n")
+                self._srv_handler.write(b"LOGOUT\n")
                 self._srv_handler.close()
             except (telnetlib.socket.error, AttributeError):
                 # The socket is already disconnected.
@@ -98,14 +98,14 @@ def _connect(self):
                                                  timeout=self._timeout)
 
             if self._login is not None:
-                self._srv_handler.write("USERNAME %s\n" % self._login)
-                result = self._srv_handler.read_until("\n", self._timeout)
+                self._srv_handler.write(b"USERNAME %s\n" % self._login.encode('utf-8'))
+                result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
                 if not result == "OK\n":
                     raise PyNUTError(result.replace("\n", ""))
 
             if self._password is not None:
-                self._srv_handler.write("PASSWORD %s\n" % self._password)
-                result = self._srv_handler.read_until("\n", self._timeout)
+                self._srv_handler.write(b"PASSWORD %s\n" % self._password.encode('utf-8'))
+                result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
                 if not result == "OK\n":
                     raise PyNUTError(result.replace("\n", ""))
         except telnetlib.socket.error:
@@ -115,8 +115,8 @@ def description(self, ups):
         """Returns the description for a given UPS."""
         logging.debug("description called...")
 
-        self._srv_handler.write("GET UPSDESC %s\n" % ups)
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"GET UPSDESC %s\n" % ups.encode('utf-8'))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         try:
             return result.split('"')[1].strip()
         except IndexError:
@@ -130,13 +130,13 @@ def list_ups(self):
         """
         logging.debug("list_ups from server")
 
-        self._srv_handler.write("LIST UPS\n")
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"LIST UPS\n")
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "BEGIN LIST UPS\n":
             raise PyNUTError(result.replace("\n", ""))
 
-        result = self._srv_handler.read_until("END LIST UPS\n",
-                                              self._timeout)
+        result = self._srv_handler.read_until(b"END LIST UPS\n",
+                                              self._timeout).decode('utf-8')
 
         ups_dict = {}
         for line in result.split("\n"):
@@ -154,13 +154,13 @@ def list_vars(self, ups):
         """
         logging.debug("list_vars called...")
 
-        self._srv_handler.write("LIST VAR %s\n" % ups)
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"LIST VAR %s\n" % ups.encode('utf-8'))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "BEGIN LIST VAR %s\n" % ups:
             raise PyNUTError(result.replace("\n", ""))
 
-        result = self._srv_handler.read_until("END LIST VAR %s\n" % ups,
-                                              self._timeout)
+        result = self._srv_handler.read_until(b"END LIST VAR %s\n" % ups.encode('utf-8'),
+                                              self._timeout).decode('utf-8')
         offset = len("VAR %s " % ups)
         end_offset = 0 - (len("END LIST VAR %s\n" % ups) + 1)
 
@@ -179,13 +179,13 @@ def list_commands(self, ups):
         """
         logging.debug("list_commands called...")
 
-        self._srv_handler.write("LIST CMD %s\n" % ups)
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"LIST CMD %s\n" % ups.encode('utf-8'))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "BEGIN LIST CMD %s\n" % ups:
             raise PyNUTError(result.replace("\n", ""))
 
-        result = self._srv_handler.read_until("END LIST CMD %s\n" % ups,
-                                              self._timeout)
+        result = self._srv_handler.read_until(b"END LIST CMD %s\n" % ups.encode('utf-8'),
+                                              self._timeout).decode('utf-8')
         offset = len("CMD %s " % ups)
         end_offset = 0 - (len("END LIST CMD %s\n" % ups) + 1)
 
@@ -195,8 +195,8 @@ def list_commands(self, ups):
 
             # For each var we try to get the available description
             try:
-                self._srv_handler.write("GET CMDDESC %s %s\n" % (ups, command))
-                temp = self._srv_handler.read_until("\n", self._timeout)
+                self._srv_handler.write(b"GET CMDDESC %s %s\n" % (ups.encode('utf-8'), command.encode('utf-8')))
+                temp = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
                 if temp.startswith("CMDDESC"):
                     desc_offset = len("CMDDESC %s %s " % (ups, command))
                     commands[command] = temp[desc_offset:-1].split('"')[1]
@@ -219,15 +219,15 @@ def list_clients(self, ups=None):
             raise PyNUTError("%s is not a valid UPS" % ups)
 
         if ups:
-            self._srv_handler.write("LIST CLIENTS %s\n" % ups)
+            self._srv_handler.write(b"LIST CLIENTS %s\n" % ups.encode('utf-8'))
         else:
-            self._srv_handler.write("LIST CLIENTS\n")
-        result = self._srv_handler.read_until("\n", self._timeout)
+            self._srv_handler.write(b"LIST CLIENTS\n")
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "BEGIN LIST CLIENTS\n":
             raise PyNUTError(result.replace("\n", ""))
 
-        result = self._srv_handler.read_until("END LIST CLIENTS\n",
-                                              self._timeout)
+        result = self._srv_handler.read_until(b"END LIST CLIENTS\n",
+                                              self._timeout).decode('utf-8')
 
         clients = {}
         for line in result.split("\n"):
@@ -247,13 +247,13 @@ def list_rw_vars(self, ups):
         """
         logging.debug("list_vars from '%s'...", ups)
 
-        self._srv_handler.write("LIST RW %s\n" % ups)
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"LIST RW %s\n" % ups.encode('utf-8'))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "BEGIN LIST RW %s\n" % ups:
             raise PyNUTError(result.replace("\n", ""))
 
-        result = self._srv_handler.read_until("END LIST RW %s\n" % ups,
-                                              self._timeout)
+        result = self._srv_handler.read_until(b"END LIST RW %s\n" % ups.encode('utf-8'),
+                                              self._timeout).decode('utf-8')
         offset = len("VAR %s" % ups)
         end_offset = 0 - (len("END LIST RW %s\n" % ups) + 1)
 
@@ -271,13 +271,13 @@ def list_enum(self, ups, var):
         """
         logging.debug("list_enum from '%s'...", ups)
 
-        self._srv_handler.write("LIST ENUM %s %s\n" % (ups, var))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"LIST ENUM %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "BEGIN LIST ENUM %s %s\n" % (ups, var):
             raise PyNUTError(result.replace("\n", ""))
 
-        result = self._srv_handler.read_until("END LIST ENUM %s %s\n" % (ups, var),
-                                              self._timeout)
+        result = self._srv_handler.read_until(b"END LIST ENUM %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8')),
+                                              self._timeout).decode('utf-8')
         offset = len("ENUM %s %s" % (ups, var))
         end_offset = 0 - (len("END LIST ENUM %s %s\n" % (ups, var)) + 1)
 
@@ -294,13 +294,13 @@ def list_range(self, ups, var):
         """
         logging.debug("list_range from '%s'...", ups)
 
-        self._srv_handler.write("LIST RANGE %s %s\n" % (ups, var))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"LIST RANGE %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "BEGIN LIST RANGE %s %s\n" % (ups, var):
             raise PyNUTError(result.replace("\n", ""))
 
-        result = self._srv_handler.read_until("END LIST RANGE %s %s\n" % (ups, var),
-                                              self._timeout)
+        result = self._srv_handler.read_until(b"END LIST RANGE %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8')),
+                                              self._timeout).decode('utf-8')
         offset = len("RANGE %s %s" % (ups, var))
         end_offset = 0 - (len("END LIST RANGE %s %s\n" % (ups, var)) + 1)
 
@@ -318,8 +318,8 @@ def set_var(self, ups, var, value):
         """
         logging.debug("set_var '%s' from '%s' to '%s'", var, ups, value)
 
-        self._srv_handler.write("SET VAR %s %s %s\n" % (ups, var, value))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"SET VAR %s %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8'), value.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "OK\n":
             raise PyNUTError(result.replace("\n", ""))
 
@@ -327,8 +327,8 @@ def get_var(self, ups, var):
         """Get the value of a variable."""
         logging.debug("get_var called...")
 
-        self._srv_handler.write("GET VAR %s %s\n" % (ups, var))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"GET VAR %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         try:
             # result = 'VAR %s %s "%s"\n' % (ups, var, value)
             return result.split('"')[1].strip()
@@ -344,8 +344,8 @@ def var_description(self, ups, var):
         """Get a variable's description."""
         logging.debug("var_description called...")
 
-        self._srv_handler.write("GET DESC %s %s\n" % (ups, var))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"GET DESC %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         try:
             # result = 'DESC %s %s "%s"\n' % (ups, var, description)
             return result.split('"')[1].strip()
@@ -356,8 +356,8 @@ def var_type(self, ups, var):
         """Get a variable's type."""
         logging.debug("var_type called...")
 
-        self._srv_handler.write("GET TYPE %s %s\n" % (ups, var))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"GET TYPE %s %s\n" % (ups.encode('utf-8'), var.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         try:
             # result = 'TYPE %s %s %s\n' % (ups, var, type)
             type_ = ' '.join(result.split(' ')[3:]).strip()
@@ -372,8 +372,8 @@ def command_description(self, ups, command):
         """Get a command's description."""
         logging.debug("command_description called...")
 
-        self._srv_handler.write("GET CMDDESC %s %s\n" % (ups, command))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"GET CMDDESC %s %s\n" % (ups.encode('utf-8'), command.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         try:
             # result = 'CMDDESC %s %s "%s"' % (ups, command, description)
             return result.split('"')[1].strip()
@@ -384,8 +384,8 @@ def run_command(self, ups, command):
         """Send a command to the specified UPS."""
         logging.debug("run_command called...")
 
-        self._srv_handler.write("INSTCMD %s %s\n" % (ups, command))
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"INSTCMD %s %s\n" % (ups.encode('utf-8'), command.encode('utf-8')))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "OK\n":
             raise PyNUTError(result.replace("\n", ""))
 
@@ -393,14 +393,14 @@ def fsd(self, ups):
         """Send MASTER and FSD commands."""
         logging.debug("MASTER called...")
 
-        self._srv_handler.write("MASTER %s\n" % ups)
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"MASTER %s\n" % ups.encode('utf-8'))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "OK MASTER-GRANTED\n":
             raise PyNUTError(("Master level function are not available", ""))
 
         logging.debug("FSD called...")
-        self._srv_handler.write("FSD %s\n" % ups)
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"FSD %s\n" % ups.encode('utf-8'))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         if result != "OK FSD-SET\n":
             raise PyNUTError(result.replace("\n", ""))
 
@@ -410,8 +410,8 @@ def num_logins(self, ups):
         """
         logging.debug("num_logins called on '%s'...", ups)
 
-        self._srv_handler.write("GET NUMLOGINS %s\n" % ups)
-        result = self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"GET NUMLOGINS %s\n" % ups.encode('utf-8'))
+        result = self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
         try:
             # result = "NUMLOGINS %s %s\n" % (ups, int(numlogins))
             return int(result.split(' ')[2].strip())
@@ -422,12 +422,12 @@ def help(self):
         """Send HELP command."""
         logging.debug("HELP called...")
 
-        self._srv_handler.write("HELP\n")
-        return self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"HELP\n")
+        return self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
 
     def ver(self):
         """Send VER command."""
         logging.debug("VER called...")
 
-        self._srv_handler.write("VER\n")
-        return self._srv_handler.read_until("\n", self._timeout)
+        self._srv_handler.write(b"VER\n")
+        return self._srv_handler.read_until(b"\n", self._timeout).decode('utf-8')
diff --git a/tests/mockserver.py b/tests/mockserver.py
index d782e52..ead4d04 100644
--- a/tests/mockserver.py
+++ b/tests/mockserver.py
@@ -3,8 +3,8 @@
 class MockServer(object):
     def __init__(self, host=None, port=None, broken=True, ok=True,
             broken_username=False, timeout=None):
-        self.valid = "test"
-        self.valid_desc = '"Test UPS 1"'
+        self.valid = b"test"
+        self.valid_desc = b'"Test UPS 1"'
         self.broken = broken
         self.ok = ok
         self.broken_username = broken_username
@@ -20,115 +20,115 @@ def close(self):
         pass
 
     def run_command(self):
-        if self.broken and not self.broken_username and self.command == "USERNAME %s\n" % self.valid:
-            return 'OK\n'
+        if self.broken and not self.broken_username and self.command == b"USERNAME %s\n" % self.valid:
+            return b'OK\n'
         elif self.broken:
-            return 'ERR\n'
-        elif self.command == "HELP\n":
-            return 'Commands: HELP VER GET LIST SET INSTCMD LOGIN LOGOUT USERNAME PASSWORD STARTTLS\n'
-        elif self.command == "VER\n":
-            return 'Network UPS Tools upsd 2.7.1 - http://www.networkupstools.org/\n'
-        elif self.command == "GET CMDDESC %s %s\n" % (self.valid, self.valid):
-            return 'CMDDESC '+self.valid+' '+self.valid+' '+self.valid_desc+'\n'
-        elif self.command == "LIST UPS\n" and self.first:
+            return b'ERR\n'
+        elif self.command == b"HELP\n":
+            return b'Commands: HELP VER GET LIST SET INSTCMD LOGIN LOGOUT USERNAME PASSWORD STARTTLS\n'
+        elif self.command == b"VER\n":
+            return b'Network UPS Tools upsd 2.7.1 - http://www.networkupstools.org/\n'
+        elif self.command == b"GET CMDDESC %s %s\n" % (self.valid, self.valid):
+            return b'CMDDESC '+self.valid+b' '+self.valid+b' '+self.valid_desc+b'\n'
+        elif self.command == b"LIST UPS\n" and self.first:
             self.first = False
-            return 'BEGIN LIST UPS\n'
-        elif self.command == "LIST UPS\n":
-            return 'UPS '+self.valid+' '+self.valid_desc+'\nUPS Test_UPS2 "Test UPS 2"\nEND LIST UPS\n'
-        elif self.command == "LIST VAR %s\n" % self.valid and self.first:
+            return b'BEGIN LIST UPS\n'
+        elif self.command == b"LIST UPS\n":
+            return b'UPS '+self.valid+b' '+self.valid_desc+b'\nUPS Test_UPS2 "Test UPS 2"\nEND LIST UPS\n'
+        elif self.command == b"LIST VAR %s\n" % self.valid and self.first:
             self.first = False
-            return 'BEGIN LIST VAR '+self.valid+'\n'
-        elif self.command == "LIST VAR %s\n" % self.valid:
-            return 'VAR '+self.valid+' battery.charge "100"\nVAR '+self.valid+' battery.voltage "14.44"\nEND LIST VAR '+self.valid+'\n'
-        elif self.command.startswith("LIST VAR"):
-            return 'ERR INVALID-ARGUMENT\n'
-        elif self.command == "LIST CMD %s\n" % self.valid and self.first:
+            return b'BEGIN LIST VAR '+self.valid+b'\n'
+        elif self.command == b"LIST VAR %s\n" % self.valid:
+            return b'VAR '+self.valid+b' battery.charge "100"\nVAR '+self.valid+b' battery.voltage "14.44"\nEND LIST VAR '+self.valid+b'\n'
+        elif self.command.startswith(b"LIST VAR"):
+            return b'ERR INVALID-ARGUMENT\n'
+        elif self.command == b"LIST CMD %s\n" % self.valid and self.first:
             self.first = False
-            return 'BEGIN LIST CMD '+self.valid+'\n'
-        elif self.command == "LIST CMD %s\n" % self.valid:
-            return 'CMD '+self.valid+' '+self.valid+'\nEND LIST CMD '+self.valid+'\n'
-        elif self.command.startswith("LIST CMD"):
-            return 'ERR INVALID-ARGUMENT\n'
-        elif self.command == "LIST RW %s\n" % self.valid and self.first:
+            return b'BEGIN LIST CMD '+self.valid+b'\n'
+        elif self.command == b"LIST CMD %s\n" % self.valid:
+            return b'CMD '+self.valid+b' '+self.valid+b'\nEND LIST CMD '+self.valid+b'\n'
+        elif self.command.startswith(b"LIST CMD"):
+            return b'ERR INVALID-ARGUMENT\n'
+        elif self.command == b"LIST RW %s\n" % self.valid and self.first:
             self.first = False
-            return 'BEGIN LIST RW '+self.valid+'\n'
-        elif self.command == "LIST RW %s\n" % self.valid:
-            return 'RW '+self.valid+' '+self.valid+' "test"\nEND LIST RW '+self.valid+'\n'
-        elif self.command.startswith("LIST RW"):
-            return 'ERR INVALID-ARGUMENT\n'
-        elif self.command == "LIST CLIENTS %s\n" % self.valid and self.first:
+            return b'BEGIN LIST RW '+self.valid+b'\n'
+        elif self.command == b"LIST RW %s\n" % self.valid:
+            return b'RW '+self.valid+b' '+self.valid+b' "test"\nEND LIST RW '+self.valid+b'\n'
+        elif self.command.startswith(b"LIST RW"):
+            return b'ERR INVALID-ARGUMENT\n'
+        elif self.command == b"LIST CLIENTS %s\n" % self.valid and self.first:
             self.first = False
-            return 'BEGIN LIST CLIENTS\n'
-        elif self.command == "LIST CLIENTS %s\n" % self.valid:
-            return 'CLIENT '+self.valid+' '+self.valid+'\nEND LIST CLIENTS\n'
-        elif self.command.startswith("LIST CLIENTS"):
-            return 'ERR INVALID-ARGUMENT\n'
-        elif self.command == "LIST ENUM %s %s\n" % (self.valid, self.valid) and self.first:
+            return b'BEGIN LIST CLIENTS\n'
+        elif self.command == b"LIST CLIENTS %s\n" % self.valid:
+            return b'CLIENT '+self.valid+b' '+self.valid+b'\nEND LIST CLIENTS\n'
+        elif self.command.startswith(b"LIST CLIENTS"):
+            return b'ERR INVALID-ARGUMENT\n'
+        elif self.command == b"LIST ENUM %s %s\n" % (self.valid, self.valid) and self.first:
             self.first = False
-            return 'BEGIN LIST ENUM %s %s\n' % (self.valid, self.valid)
-        elif self.command == "LIST ENUM %s %s\n" % (self.valid, self.valid):
-            return 'ENUM %s %s %s\nEND LIST ENUM %s %s\n' % (self.valid,
+            return b'BEGIN LIST ENUM %s %s\n' % (self.valid, self.valid)
+        elif self.command == b"LIST ENUM %s %s\n" % (self.valid, self.valid):
+            return b'ENUM %s %s %s\nEND LIST ENUM %s %s\n' % (self.valid,
                     self.valid, self.valid_desc, self.valid, self.valid)
-        elif self.command == "LIST RANGE %s %s\n" % (self.valid, self.valid) and self.first:
+        elif self.command == b"LIST RANGE %s %s\n" % (self.valid, self.valid) and self.first:
             self.first = False
-            return 'BEGIN LIST RANGE %s %s\n' % (self.valid, self.valid)
-        elif self.command == "LIST RANGE %s %s\n" % (self.valid, self.valid):
-            return 'RANGE %s %s %s %s\nEND LIST RANGE %s %s\n' % (self.valid,
+            return b'BEGIN LIST RANGE %s %s\n' % (self.valid, self.valid)
+        elif self.command == b"LIST RANGE %s %s\n" % (self.valid, self.valid):
+            return b'RANGE %s %s %s %s\nEND LIST RANGE %s %s\n' % (self.valid,
                     self.valid, self.valid_desc, self.valid_desc, self.valid, self.valid)
-        elif self.command == "SET VAR %s %s %s\n" % (self.valid, self.valid, self.valid):
-            return 'OK\n'
-        elif self.command.startswith("SET"):
-            return 'ERR ACCESS-DENIED\n'
-        elif self.command == "INSTCMD %s %s\n"% (self.valid, self.valid):
-            return 'OK\n'
-        elif self.command.startswith("INSTCMD"):
-            return 'ERR CMD-NOT-SUPPORTED\n'
+        elif self.command == b"SET VAR %s %s %s\n" % (self.valid, self.valid, self.valid):
+            return b'OK\n'
+        elif self.command.startswith(b"SET"):
+            return b'ERR ACCESS-DENIED\n'
+        elif self.command == b"INSTCMD %s %s\n"% (self.valid, self.valid):
+            return b'OK\n'
+        elif self.command.startswith(b"INSTCMD"):
+            return b'ERR CMD-NOT-SUPPORTED\n'
         # TODO: LOGIN/LOGOUT commands
-        elif self.command == "USERNAME %s\n" % self.valid:
-            return 'OK\n'
-        elif self.command.startswith("USERNAME"):
-            return 'ERR\n'  # FIXME: What does it say on invalid password?
-        elif self.command == "PASSWORD %s\n" % self.valid:
-            return 'OK\n'
-        elif self.command.startswith("PASSWORD"):
-            return 'ERR\n'  # FIXME: ^
-        elif self.command == "STARTTLS\n":
-            return 'ERR FEATURE-NOT-CONFIGURED\n'
-        elif self.command == "MASTER %s\n" % self.valid:
-            return 'OK MASTER-GRANTED\n'
-        elif self.command == "FSD %s\n" % self.valid and self.ok:
-            return 'OK FSD-SET\n'
-        elif self.command == "FSD %s\n" % self.valid:
-            return 'ERR\n'
-        elif self.command == "GET NUMLOGINS %s\n" % self.valid:
-            return 'NUMLOGINS %s 1\n' % self.valid
-        elif self.command.startswith("GET NUMLOGINS"):
-            return 'ERR UNKNOWN-UPS\n'
-        elif self.command == "GET UPSDESC %s\n" % self.valid:
-            return 'UPSDESC %s %s\n' % (self.valid, self.valid_desc)
-        elif self.command.startswith("GET UPSDESC"):
-            return 'ERR UNKNOWN-UPS\n'
-        elif self.command == "GET VAR %s %s\n" % (self.valid, self.valid):
-            return 'VAR %s %s "100"\n' % (self.valid, self.valid)
-        elif self.command.startswith("GET VAR %s" % self.valid):
-            return 'ERR VAR-NOT-SUPPORTED\n'
-        elif self.command.startswith("GET VAR "):
-            return 'ERR UNKNOWN-UPS\n'
-        elif self.command.startswith("GET VAR"):
-            return 'ERR INVALID-ARGUMENT\n'
-        elif self.command == "GET TYPE %s %s\n" % (self.valid, self.valid):
-            return 'TYPE %s %s RW STRING:3\n' % (self.valid, self.valid)
-        elif self.command.startswith("GET TYPE %s" % self.valid):
-            return 'ERR VAR-NOT-SUPPORTED\n'
-        elif self.command.startswith("GET TYPE"):
-            return 'ERR INVALID-ARGUMENT\n'
-        elif self.command == "GET DESC %s %s\n" % (self.valid, self.valid):
-            return 'DESC %s %s %s\n' % (self.valid, self.valid, self.valid_desc)
-        elif self.command.startswith("GET DESC"):
-            return 'ERR-INVALID-ARGUMENT\n'
-        elif self.command == "GET CMDDESC %s %s" % (self.valid, self.valid):
-            return 'CMDDESC %s %s %s\n' % (self.valid, self.valid, self.valid_desc)
-        elif self.command.startswith("GET CMDDESC"):
-            return 'ERR INVALID-ARGUMENT'
+        elif self.command == b"USERNAME %s\n" % self.valid:
+            return b'OK\n'
+        elif self.command.startswith(b"USERNAME"):
+            return b'ERR\n'  # FIXME: What does it say on invalid password?
+        elif self.command == b"PASSWORD %s\n" % self.valid:
+            return b'OK\n'
+        elif self.command.startswith(b"PASSWORD"):
+            return b'ERR\n'  # FIXME: ^
+        elif self.command == b"STARTTLS\n":
+            return b'ERR FEATURE-NOT-CONFIGURED\n'
+        elif self.command == b"MASTER %s\n" % self.valid:
+            return b'OK MASTER-GRANTED\n'
+        elif self.command == b"FSD %s\n" % self.valid and self.ok:
+            return b'OK FSD-SET\n'
+        elif self.command == b"FSD %s\n" % self.valid:
+            return b'ERR\n'
+        elif self.command == b"GET NUMLOGINS %s\n" % self.valid:
+            return b'NUMLOGINS %s 1\n' % self.valid
+        elif self.command.startswith(b"GET NUMLOGINS"):
+            return b'ERR UNKNOWN-UPS\n'
+        elif self.command == b"GET UPSDESC %s\n" % self.valid:
+            return b'UPSDESC %s %s\n' % (self.valid, self.valid_desc)
+        elif self.command.startswith(b"GET UPSDESC"):
+            return b'ERR UNKNOWN-UPS\n'
+        elif self.command == b"GET VAR %s %s\n" % (self.valid, self.valid):
+            return b'VAR %s %s "100"\n' % (self.valid, self.valid)
+        elif self.command.startswith(b"GET VAR %s" % self.valid):
+            return b'ERR VAR-NOT-SUPPORTED\n'
+        elif self.command.startswith(b"GET VAR "):
+            return b'ERR UNKNOWN-UPS\n'
+        elif self.command.startswith(b"GET VAR"):
+            return b'ERR INVALID-ARGUMENT\n'
+        elif self.command == b"GET TYPE %s %s\n" % (self.valid, self.valid):
+            return b'TYPE %s %s RW STRING:3\n' % (self.valid, self.valid)
+        elif self.command.startswith(b"GET TYPE %s" % self.valid):
+            return b'ERR VAR-NOT-SUPPORTED\n'
+        elif self.command.startswith(b"GET TYPE"):
+            return b'ERR INVALID-ARGUMENT\n'
+        elif self.command == b"GET DESC %s %s\n" % (self.valid, self.valid):
+            return b'DESC %s %s %s\n' % (self.valid, self.valid, self.valid_desc)
+        elif self.command.startswith(b"GET DESC"):
+            return b'ERR-INVALID-ARGUMENT\n'
+        elif self.command == b"GET CMDDESC %s %s" % (self.valid, self.valid):
+            return b'CMDDESC %s %s %s\n' % (self.valid, self.valid, self.valid_desc)
+        elif self.command.startswith(b"GET CMDDESC"):
+            return b'ERR INVALID-ARGUMENT'
         else:
-            return 'ERR UNKNOWN-COMMAND\n'
+            return b'ERR UNKNOWN-COMMAND\n'