diff --git a/src/calibre/utils/winreg/default_programs.py b/src/calibre/utils/winreg/default_programs.py
index 4c3e37ac2a..79186cd678 100644
--- a/src/calibre/utils/winreg/default_programs.py
+++ b/src/calibre/utils/winreg/default_programs.py
@@ -163,4 +163,6 @@ class Register(Thread):
 
 if __name__ == '__main__':
     del sys.path[0]
-    unregister()
+    func = (register if sys.argv[-1] == 'register' else unregister)
+    print ('Running', func.__name__, '...')
+    func()