diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
index f3999f5e8091..58e58a32e93d 100644
--- a/drivers/staging/comedi/comedidev.h
+++ b/drivers/staging/comedi/comedidev.h
@@ -253,6 +253,7 @@ struct comedi_device {
 	struct comedi_subdevice *subdevices;
 
 	/* dumb */
+	void __iomem *mmio;
 	unsigned long iobase;
 	unsigned long iolen;
 	unsigned int irq;
diff --git a/drivers/staging/comedi/drivers.c b/drivers/staging/comedi/drivers.c
index 42ddf1332ce8..9ada130f2a76 100644
--- a/drivers/staging/comedi/drivers.c
+++ b/drivers/staging/comedi/drivers.c
@@ -121,6 +121,7 @@ static void comedi_device_detach_cleanup(struct comedi_device *dev)
 	dev->driver = NULL;
 	dev->board_name = NULL;
 	dev->board_ptr = NULL;
+	dev->mmio = NULL;
 	dev->iobase = 0;
 	dev->iolen = 0;
 	dev->ioenabled = false;