diff --git a/src/calibre/gui2/save.py b/src/calibre/gui2/save.py
index 0593be6d64..3c0d71b305 100644
--- a/src/calibre/gui2/save.py
+++ b/src/calibre/gui2/save.py
@@ -158,7 +158,7 @@ class Saver(QObject):
             except Failure as err:
                 error_dialog(self.pd, _('Critical failure'), _(
                     'Could not save books to disk, click "Show details" for more information'),
-                    det_msg=unicode_type(err.failure_message) + '\n' + unicode_type(err.details), show=True)
+                    det_msg=force_unicode(err.failure_message) + '\n' + force_unicode(err.details), show=True)
                 self.pd.canceled = True
         self.do_one_signal.emit()
 
diff --git a/src/calibre/utils/ipc/server.py b/src/calibre/utils/ipc/server.py
index cf8d558d88..47e40b44b0 100644
--- a/src/calibre/utils/ipc/server.py
+++ b/src/calibre/utils/ipc/server.py
@@ -18,7 +18,7 @@ from math import ceil
 from multiprocessing.connection import Listener, arbitrary_address
 from threading import RLock, Thread
 
-from calibre import detect_ncpus as cpu_count
+from calibre import detect_ncpus as cpu_count, force_unicode
 from calibre.constants import DEBUG, islinux, iswindows, ispy3
 from calibre.ptempfile import base_dir
 from calibre.utils.ipc import eintr_retry_call
@@ -228,7 +228,7 @@ class Server(Thread):
               }
         cw = self.do_launch(env, gui, redirect_output, rfile, job_name=job_name)
         if isinstance(cw, string_or_bytes):
-            raise CriticalError('Failed to launch worker process:\n'+cw)
+            raise CriticalError('Failed to launch worker process:\n'+force_unicode(cw))
         if DEBUG:
             print('Worker Launch took:', time.time() - start)
         return cw