diff --git a/masque/builder/device_library.py b/masque/builder/device_library.py
index d86a6cc..8e0cf40 100644
--- a/masque/builder/device_library.py
+++ b/masque/builder/device_library.py
@@ -22,7 +22,7 @@ DL2 = TypeVar('DL2', bound='LazyDeviceLibrary')
 LDL = TypeVar('LDL', bound='LibDeviceLibrary')
 
 
-class LazyDeviceLibrary:
+class LazyDeviceLibrary(Mapping[str, DeviceRef]):
     """
     This class maps names to functions which generate or load the
      relevant `Device` object.
@@ -61,7 +61,7 @@ class LazyDeviceLibrary:
         return iter(self.keys())
 
     def __repr__(self) -> str:
-        return '<LazyDeviceLibrary with keys ' + repr(list(self.generators.keys())) + '>'
+        return '<LazyDeviceLibrary with keys ' + repr(list(self.keys())) + '>'
 
     def get_device(self, key: str) -> Device:
         if self.enable_cache and key in self.cache:
diff --git a/masque/shapes/shape.py b/masque/shapes/shape.py
index 9eae34d..66f83db 100644
--- a/masque/shapes/shape.py
+++ b/masque/shapes/shape.py
@@ -15,9 +15,11 @@ if TYPE_CHECKING:
 
 
 # Type definitions
-normalized_shape_tuple = Tuple[Tuple,
-                               Tuple[NDArray[numpy.float64], float, float, bool, float],
-                               Callable[[], 'Shape']]
+normalized_shape_tuple = Tuple[
+    Tuple,
+    Tuple[NDArray[numpy.float64], float, float, bool, float],
+    Callable[[], 'Shape'],
+    ]
 
 # ## Module-wide defaults
 # Default number of points per polygon for shapes