diff --git a/src/tape_drivers/freebsd/cam/cam_tc.c b/src/tape_drivers/freebsd/cam/cam_tc.c
index 7c7f82bd..bfe785a2 100644
--- a/src/tape_drivers/freebsd/cam/cam_tc.c
+++ b/src/tape_drivers/freebsd/cam/cam_tc.c
@@ -281,7 +281,7 @@ int camtape_open(const char *devname, void **handle)
 	/* Check the drive is supportable */
 	softc->vendor = get_vendor_id(vendor);
 	struct supported_device **cur = get_supported_devs(softc->vendor);
-	while(*cur) {
+	while(cur && *cur) {
 		if ((! strncmp((char*)softc->cd->inq_data.vendor, (*cur)->vendor_id,
 					   strlen((*cur)->vendor_id)) ) &&
 		   (! strncmp((char*)softc->cd->inq_data.product, (*cur)->product_id,
diff --git a/src/tape_drivers/linux/sg/sg_tape.c b/src/tape_drivers/linux/sg/sg_tape.c
index 8a13493e..cd9b533a 100644
--- a/src/tape_drivers/linux/sg/sg_tape.c
+++ b/src/tape_drivers/linux/sg/sg_tape.c
@@ -500,7 +500,7 @@ static int _raw_open(struct sg_data *priv)
 	priv->vendor = get_vendor_id(id_data.vendor_id);
 
 	struct supported_device **cur = get_supported_devs(priv->vendor);
-	while(*cur) {
+	while(cur && *cur) {
 		if((! strncmp(id_data.vendor_id, (*cur)->vendor_id, strlen((*cur)->vendor_id)) ) &&
 		   (! strncmp(id_data.product_id, (*cur)->product_id, strlen((*cur)->product_id)) ) ) {
 			drive_type = (*cur)->drive_type;