diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index df87fe1640..5628b7e02d 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -108,9 +108,13 @@ else:
 DEBUG = hasenv('CALIBRE_DEBUG')
 
 
-def debug():
+def debug(val=True):
     global DEBUG
-    DEBUG = True
+    DEBUG = bool(val)
+
+
+def is_debugging():
+    return DEBUG
 
 
 def _get_cache_dir():
diff --git a/src/calibre/devices/__init__.py b/src/calibre/devices/__init__.py
index ecbe784aee..f958b4684f 100644
--- a/src/calibre/devices/__init__.py
+++ b/src/calibre/devices/__init__.py
@@ -70,7 +70,7 @@ def debug(ioreg_to_tmp=False, buf=None, plugins=None,
     from calibre.customize.ui import device_plugins, disabled_device_plugins
     from calibre.debug import print_basic_debug_info
     from calibre.devices.scanner import DeviceScanner
-    from calibre.constants import iswindows, ismacos
+    from calibre.constants import iswindows, ismacos, debug, is_debugging
     from calibre import prints
     from polyglot.io import PolyglotStringIO
     oldo, olde = sys.stdout, sys.stderr
@@ -92,6 +92,8 @@ def debug(ioreg_to_tmp=False, buf=None, plugins=None,
     if disabled_plugins is None:
         disabled_plugins = list(disabled_device_plugins())
 
+    orig_debug = is_debugging()
+    debug(True)
     try:
         print_basic_debug_info(out=buf)
         s = DeviceScanner()
@@ -187,6 +189,7 @@ def debug(ioreg_to_tmp=False, buf=None, plugins=None,
         if hasattr(buf, 'getvalue'):
             return buf.getvalue()
     finally:
+        debug(orig_debug)
         sys.stdout = oldo
         sys.stderr = olde
         if plugins is None:
diff --git a/src/calibre/devices/usbms/device.py b/src/calibre/devices/usbms/device.py
index 0958b6eefc..c8700ac756 100644
--- a/src/calibre/devices/usbms/device.py
+++ b/src/calibre/devices/usbms/device.py
@@ -19,7 +19,7 @@ from collections import namedtuple
 from itertools import repeat
 
 from calibre import prints
-from calibre.constants import DEBUG, isfreebsd, islinux, ismacos, iswindows
+from calibre.constants import is_debugging, isfreebsd, islinux, ismacos, iswindows
 from calibre.devices.errors import DeviceError
 from calibre.devices.interface import DevicePlugin
 from calibre.devices.usbms.deviceconfig import DeviceConfig
@@ -236,7 +236,7 @@ class Device(DeviceConfig, DevicePlugin):
         from calibre.devices.scanner import drive_is_ok
         from calibre.devices.winusb import get_drive_letters_for_device
         usbdev = self.device_being_opened
-        debug = DEBUG or getattr(self, 'do_device_debug', False)
+        debug = is_debugging() or getattr(self, 'do_device_debug', False)
         try:
             dlmap = get_drive_letters_for_device(usbdev, debug=debug)
         except Exception:
@@ -394,7 +394,7 @@ class Device(DeviceConfig, DevicePlugin):
         drives = self.osx_sort_names(bsd_drives.copy())
         mount_map = get_mounted_filesystems()
         drives = {k: mount_map.get(v) for k, v in iteritems(drives)}
-        if DEBUG:
+        if is_debugging():
             print()
             from pprint import pprint
             pprint({'bsd_drives': bsd_drives, 'mount_map': mount_map, 'drives': drives})
@@ -501,7 +501,7 @@ class Device(DeviceConfig, DevicePlugin):
                             ok[node] = False
                     except:
                         ok[node] = False
-                    if DEBUG and not ok[node]:
+                    if is_debugging() and not ok[node]:
                         print(f'\nIgnoring the node: {node} as could not read size from: {sz}')
 
                     devnodes.append(node)
@@ -568,7 +568,7 @@ class Device(DeviceConfig, DevicePlugin):
             'the device has already been ejected, or your '
             'kernel is exporting a deprecated version of SYSFS.')
                     %self.__class__.__name__)
-        if DEBUG:
+        if is_debugging():
             print('\nFound device nodes:', main, carda, cardb)
 
         self._linux_mount_map = {}
@@ -614,7 +614,7 @@ class Device(DeviceConfig, DevicePlugin):
                     os.remove(path)
                 except:
                     pass
-            if DEBUG and ro:
+            if is_debugging() and ro:
                 print('\nThe mountpoint', mp, 'is readonly, ignoring it')
             return ro
 
diff --git a/src/calibre/devices/usbms/driver.py b/src/calibre/devices/usbms/driver.py
index ba4c10ce15..d281439f8d 100644
--- a/src/calibre/devices/usbms/driver.py
+++ b/src/calibre/devices/usbms/driver.py
@@ -13,7 +13,7 @@ from itertools import cycle
 
 from calibre.constants import numeric_version, ismacos
 from calibre import prints, isbytestring, fsync
-from calibre.constants import filesystem_encoding, DEBUG
+from calibre.constants import filesystem_encoding, is_debugging
 from calibre.devices.usbms.cli import CLI
 from calibre.devices.usbms.device import Device
 from calibre.devices.usbms.books import BookList, Book
@@ -25,7 +25,7 @@ def debug_print(*args, **kw):
     base_time = getattr(debug_print, 'base_time', None)
     if base_time is None:
         debug_print.base_time = base_time = time.monotonic()
-    if DEBUG:
+    if is_debugging():
         prints('DEBUG: %6.1f'%(time.monotonic()-base_time), *args, **kw)