diff --git a/drivers/staging/comedi/drivers/jr3_pci.c b/drivers/staging/comedi/drivers/jr3_pci.c
index 0d2c2eb..bd39784 100644
--- a/drivers/staging/comedi/drivers/jr3_pci.c
+++ b/drivers/staging/comedi/drivers/jr3_pci.c
@@ -849,8 +849,11 @@
 	}
 
 	devpriv->pci_enabled = 1;
-	devpriv->iobase =
-	    ioremap(pci_resource_start(card, 0), sizeof(struct jr3_t));
+	devpriv->iobase = ioremap(pci_resource_start(card, 0),
+			offsetof(struct jr3_t, channel[devpriv->n_channels]));
+	if (!devpriv->iobase)
+		return -ENOMEM;
+
 	result = alloc_subdevices(dev, devpriv->n_channels);
 	if (result < 0)
 		goto out;