diff --git a/sys/dev/disk/nata/atapi-cd.c b/sys/dev/disk/nata/atapi-cd.c
--- a/sys/dev/disk/nata/atapi-cd.c
+++ b/sys/dev/disk/nata/atapi-cd.c
@@ -721,6 +721,10 @@
 	break;
 
     case CDRIOCSETBLOCKSIZE:
+	if (*(int *)ap->a_data <= 0) {
+	    error = EINVAL;
+	    break;
+	}
 	cdp->block_size = *(int *)ap->a_data;
 	acd_set_ioparm(dev);
 	break;