diff --git a/masque/library/device_library.py b/masque/library/device_library.py
index 554590e..4f8de3a 100644
--- a/masque/library/device_library.py
+++ b/masque/library/device_library.py
@@ -16,8 +16,8 @@ from .. import Pattern
 logger = logging.getLogger(__name__)
 
 
-L = TypeVar('L', bound='DeviceLibrary')
-D = TypeVar('D', bound='LibDeviceLibrary')
+D = TypeVar('D', bound='DeviceLibrary')
+L = TypeVar('L', bound='LibDeviceLibrary')
 
 
 class DeviceLibrary: