diff --git a/src/calibre/rpdb.py b/src/calibre/rpdb.py
index 1a60f3b489..4243ce6fd3 100644
--- a/src/calibre/rpdb.py
+++ b/src/calibre/rpdb.py
@@ -6,10 +6,9 @@ __license__ = 'GPL v3'
 __copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
 
 import pdb, socket, inspect, sys, select, os, atexit, time
+from contextlib import suppress
 
-from calibre import prints
 from calibre.constants import cache_dir
-from polyglot.builtins import range, raw_input as rinput
 
 PROMPT = '(debug) '
 QUESTION = '\x00\x01\x02'
@@ -18,24 +17,24 @@ QUESTION = '\x00\x01\x02'
 class RemotePdb(pdb.Pdb):
 
     def __init__(self, addr="127.0.0.1", port=4444, skip=None):
-        try:
-            prints("pdb is running on %s:%d" % (addr, port), file=sys.stderr)
-        except IOError:
-            pass
-
         # Open a reusable socket to allow for reloads
         self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True)
         self.sock.bind((addr, port))
         self.sock.listen(1)
+        with suppress(OSError):
+            print("pdb is running on %s:%d" % (addr, port), file=sys.stderr)
         clientsocket, address = self.sock.accept()
+        clientsocket.setblocking(True)
+        self.clientsocket = clientsocket
         self.handle = clientsocket.makefile('rw')
         pdb.Pdb.__init__(self, completekey='tab', stdin=self.handle, stdout=self.handle, skip=skip)
         self.prompt = PROMPT
 
     def prints(self, *args, **kwargs):
         kwargs['file'] = self.handle
-        prints(*args, **kwargs)
+        kwargs['flush'] = True
+        print(*args, **kwargs)
 
     def ask_question(self, query):
         self.handle.write(QUESTION)
@@ -47,7 +46,9 @@ class RemotePdb(pdb.Pdb):
     def end_session(self, *args):
         self.clear_all_breaks()
         self.reset()
-        del self.handle
+        self.handle.close()
+        self.clientsocket.shutdown(socket.SHUT_RDWR)
+        self.clientsocket.close()
         try:
             self.sock.shutdown(socket.SHUT_RDWR)
             self.sock.close()
@@ -85,15 +86,15 @@ def set_trace(port=4444, skip=None):
         debugger = RemotePdb(port=port, skip=skip)
         debugger.set_trace(frame)
     except KeyboardInterrupt:
-        prints('Debugging aborted by keyboard interrupt')
+        print('Debugging aborted by keyboard interrupt')
     except Exception:
-        prints('Failed to run debugger')
+        print('Failed to run debugger')
         import traceback
         traceback.print_exc()
 
 
 def cli(port=4444):
-    prints('Connecting to remote debugger on port %d...' % port)
+    print('Connecting to remote debugger on port %d...' % port)
     sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     for i in range(20):
         try:
@@ -106,48 +107,51 @@ def cli(port=4444):
         try:
             sock.connect(('127.0.0.1', port))
         except socket.error as err:
-            prints('Failed to connect to remote debugger:', err, file=sys.stderr)
+            print('Failed to connect to remote debugger:', err, file=sys.stderr)
             raise SystemExit(1)
-    prints('Connected to remote process')
-    import readline
-    histfile = os.path.join(cache_dir(), 'rpdb.history')
+    print('Connected to remote process', flush=True)
     try:
-        readline.read_history_file(histfile)
-    except IOError:
+        import readline
+        histfile = os.path.join(cache_dir(), 'rpdb.history')
+        try:
+            readline.read_history_file(histfile)
+        except IOError:
+            pass
+        atexit.register(readline.write_history_file, histfile)
+        p = pdb.Pdb()
+        readline.set_completer(p.complete)
+        readline.parse_and_bind("tab: complete")
+    except ImportError:
         pass
-    atexit.register(readline.write_history_file, histfile)
-    p = pdb.Pdb()
-    readline.set_completer(p.complete)
-    readline.parse_and_bind("tab: complete")
-    sockf = sock.makefile('rw')
-
-    try:
+    sock.setblocking(True)
+    with suppress(KeyboardInterrupt):
+        end_of_input = PROMPT.encode('utf-8')
         while True:
-            recvd = ''
-            while not recvd.endswith(PROMPT) or select.select([sock], [], [], 0) == ([sock], [], []):
-                buf = sockf.read()
+            recvd = b''
+            while select.select([sock], [], [], 0)[0] or not recvd.endswith(end_of_input):
+                buf = sock.recv(4096)
                 if not buf:
                     return
                 recvd += buf
+            recvd = recvd.decode('utf-8', 'replace')
             recvd = recvd[:-len(PROMPT)]
+            raw = ''
             if recvd.startswith(QUESTION):
                 recvd = recvd[len(QUESTION):]
-                sys.stdout.write(recvd)
+                print(recvd, end='', flush=True)
                 raw = sys.stdin.readline() or 'n'
             else:
-                sys.stdout.write(recvd)
-                raw = ''
+                print(recvd, end='', flush=True)
                 try:
-                    raw = rinput(PROMPT.decode('utf-8'))
+                    raw = input(PROMPT)
                 except (EOFError, KeyboardInterrupt):
                     pass
                 else:
                     raw += '\n'
                 if not raw:
                     raw = 'quit\n'
-            sockf.write(raw)
-    except KeyboardInterrupt:
-        pass
+            if raw:
+                sock.sendall(raw.encode('utf-8'))
 
 
 if __name__ == '__main__':