diff --git a/lib/logger/log_device.rb b/lib/logger/log_device.rb
index fe7d54f..96d77b7 100644
--- a/lib/logger/log_device.rb
+++ b/lib/logger/log_device.rb
@@ -135,7 +135,7 @@ def check_shift_log
       end
     end
 
-    if /mswin|mingw/ =~ RUBY_PLATFORM
+    if /mswin|mingw|cygwin/ =~ RUBY_PLATFORM
       def lock_shift_log
         yield
       end
diff --git a/test/logger/test_logdevice.rb b/test/logger/test_logdevice.rb
index 2a01dab..6fefd35 100644
--- a/test/logger/test_logdevice.rb
+++ b/test/logger/test_logdevice.rb
@@ -451,7 +451,7 @@ def test_shifting_size_not_rotate_too_much
     end
   ensure
     logdev0.close
-  end unless /mswin|mingw/ =~ RUBY_PLATFORM
+  end unless /mswin|mingw|cygwin/ =~ RUBY_PLATFORM
 
   def test_shifting_midnight
     Dir.mktmpdir do |tmpdir|