diff --git a/src/calibre/devices/__init__.py b/src/calibre/devices/__init__.py
index c580923a21..b7cd66642e 100644
--- a/src/calibre/devices/__init__.py
+++ b/src/calibre/devices/__init__.py
@@ -113,7 +113,7 @@ def debug(ioreg_to_tmp=False, buf=None, plugins=None,
         ioreg = None
         if ismacos:
             from calibre.devices.usbms.device import Device
-            mount = '\n'.join(repr(x) for x in Device.osx_run_mount().splitlines())
+            mount = Device.osx_run_mount()
             drives = pprint.pformat(Device.osx_get_usb_drives())
             ioreg = 'Output from mount:\n'+mount+'\n\n'
             ioreg += 'Output from osx_get_usb_drives:\n'+drives+'\n\n'
diff --git a/src/calibre/devices/usbms/device.py b/src/calibre/devices/usbms/device.py
index 357f8fe9bb..7622baa975 100644
--- a/src/calibre/devices/usbms/device.py
+++ b/src/calibre/devices/usbms/device.py
@@ -347,8 +347,7 @@ class Device(DeviceConfig, DevicePlugin):
     def osx_run_mount(cls):
         for i in range(3):
             try:
-                return subprocess.Popen('mount',
-                                    stdout=subprocess.PIPE).communicate()[0]
+                return subprocess.Popen('mount', stdout=subprocess.PIPE).communicate()[0].decode('utf-8', 'replace')
             except OSError:  # Probably an interrupted system call
                 if i == 2:
                     raise