dev->hard_start_xmit = boomerang_start_xmit;
                /* Actually, it still should work with iommu. */
                dev->features |= NETIF_F_SG;
-               if (((hw_checksums[card_idx] == -1) && (vp->drv_flags & HAS_HWCKSM)) ||
-                                       (hw_checksums[card_idx] == 1)) {
-                               dev->features |= NETIF_F_IP_CSUM;
+               if (card_idx < MAX_UNITS &&
+                   ((hw_checksums[card_idx] == -1 && (vp->drv_flags & HAS_HWCKSM)) ||
+                               hw_checksums[card_idx] == 1)) {
+                       dev->features |= NETIF_F_IP_CSUM;
                }
        } else {
                dev->hard_start_xmit = vortex_start_xmit;
        }
 
 #if DO_ZEROCOPY
-       if (    vp->rx_csumhits &&
-                       ((vp->drv_flags & HAS_HWCKSM) == 0) &&
-                       (hw_checksums[vp->card_idx] == -1)) {
-               printk(KERN_WARNING "%s supports hardware checksums, and we're not using them!\n", dev->name);
+       if (vp->rx_csumhits &&
+           (vp->drv_flags & HAS_HWCKSM) == 0 &&
+           (vp->card_idx >= MAX_UNITS || hw_checksums[vp->card_idx] == -1)) {
+                       printk(KERN_WARNING "%s supports hardware checksums, and we're "
+                                               "not using them!\n", dev->name);
        }
 #endif