--- sniff.c
+++ sniff.c
@@ -38,7 +38,7 @@
    ldd = NULL;
    ld = 0;
    npkt = 0;
-   if (strcmp (ldname, "NULL")) /* != NULL */
+   if (ldname != NULL) /* != NULL */
      (ld=1);
 
    /* ask pcap for the network address and mask of the device */