diff --git a/src/calibre/__init__.py b/src/calibre/__init__.py
index b817290786..0c84a43eca 100644
--- a/src/calibre/__init__.py
+++ b/src/calibre/__init__.py
@@ -19,13 +19,13 @@ except EnvironmentError:
 from calibre.constants import (iswindows, ismacos, islinux, isfrozen,
         isbsd, preferred_encoding, __appname__, __version__, __author__,
         fcntl, plugins, filesystem_encoding, config_dir)
-from calibre.startup import winutil
+from calibre.startup import get_debug_executable
 from calibre.utils.icu import safe_chr
 from calibre.prints import prints
 
 if False:
     # Prevent pyflakes from complaining
-    winutil, __appname__, islinux, __version__
+    get_debug_executable, __appname__, islinux, __version__
     fcntl, isfrozen, __author__, isbsd, config_dir, plugins
 
 _mt_inited = False
diff --git a/src/calibre/startup.py b/src/calibre/startup.py
index d76601520f..6802f04862 100644
--- a/src/calibre/startup.py
+++ b/src/calibre/startup.py
@@ -24,7 +24,6 @@ builtins.__dict__['dynamic_property'] = lambda func: func(None)
 from calibre.constants import iswindows, preferred_encoding, plugins, ismacos, islinux, DEBUG, isfreebsd
 
 _run_once = False
-winutil = winutilerror = None
 
 
 def get_debug_executable():
@@ -69,8 +68,8 @@ if not _run_once:
     # Ensure that the max number of open files is at least 1024
     if iswindows:
         # See https://msdn.microsoft.com/en-us/library/6e3b887c.aspx
-        if hasattr(winutil, 'setmaxstdio'):
-            winutil.setmaxstdio(max(1024, winutil.getmaxstdio()))
+        from calibre_extensions import winutil
+        winutil.setmaxstdio(max(1024, winutil.getmaxstdio()))
     else:
         import resource
         soft, hard = resource.getrlimit(resource.RLIMIT_NOFILE)