diff --git a/adafruit_bus_device/spi_device.py b/adafruit_bus_device/spi_device.py
index ea8515e..f081bf9 100644
--- a/adafruit_bus_device/spi_device.py
+++ b/adafruit_bus_device/spi_device.py
@@ -19,7 +19,7 @@
     from busio import SPI
     from digitalio import DigitalInOut
 except ImportError:
-    pass
+    DigitalInOut = None
 
 
 __version__ = "0.0.0+auto.0"