diff --git a/include/patty/kiss.h b/include/patty/kiss.h
index 059e169..7fdc8ab 100644
--- a/include/patty/kiss.h
+++ b/include/patty/kiss.h
@@ -29,9 +29,9 @@ enum patty_kiss_command {
 
 typedef struct _patty_kiss_tnc patty_kiss_tnc;
 
-patty_kiss_tnc *patty_kiss_tnc_open_fd(int fd, size_t bufsize);
+patty_kiss_tnc *patty_kiss_tnc_open_fd(int fd);
 
-patty_kiss_tnc *patty_kiss_tnc_open(const char *device, size_t bufsize);
+patty_kiss_tnc *patty_kiss_tnc_open(const char *device);
 
 int patty_kiss_tnc_fd_unix(patty_kiss_tnc *tnc);
 
diff --git a/src/decode.c b/src/decode.c
index 3cadf79..b429467 100644
--- a/src/decode.c
+++ b/src/decode.c
@@ -17,7 +17,7 @@ static void usage(int argc, char **argv, const char *message, ...) {
         va_end(args);
     }
 
-    fprintf(stderr, "usage: %s kiss.cap\n", argv[0]);
+    fprintf(stderr, "usage: %s [/dev/ttyXX|kiss.cap]\n", argv[0]);
 
     exit(1);
 }
@@ -145,11 +145,15 @@ int main(int argc, char **argv) {
     void *buf;
     int port;
 
-    if (argc != 2) {
-        usage(argc, argv, "No TNC device provided");
+    if (argc > 2) {
+        usage(argc, argv, NULL);
     }
 
-    if ((tnc = patty_kiss_tnc_open(argv[1], PATTY_KISS_BUFSZ)) == NULL) {
+    tnc = (argc == 2)?
+        patty_kiss_tnc_open(argv[1]):
+        patty_kiss_tnc_open_fd(0);
+
+    if (tnc == NULL) {
         perror("Unable to open TNC");
 
         goto error_kiss_tnc_open;
diff --git a/src/if.c b/src/if.c
index af55fbb..9d2465e 100644
--- a/src/if.c
+++ b/src/if.c
@@ -17,7 +17,7 @@ static patty_ax25_if *create_tnc(const char *device) {
 
     memset(iface, '\0', sizeof(*iface));
 
-    if ((iface->tnc = patty_kiss_tnc_open(device, PATTY_KISS_BUFSZ)) == NULL) {
+    if ((iface->tnc = patty_kiss_tnc_open(device)) == NULL) {
         goto error_kiss_tnc_open;
     }
 
diff --git a/src/kiss.c b/src/kiss.c
index 105d94a..c405144 100644
--- a/src/kiss.c
+++ b/src/kiss.c
@@ -28,19 +28,19 @@ struct _patty_kiss_tnc {
            dropped;
 };
 
-patty_kiss_tnc *patty_kiss_tnc_open_fd(int fd, size_t bufsz) {
+patty_kiss_tnc *patty_kiss_tnc_open_fd(int fd) {
     patty_kiss_tnc *tnc;
 
     if ((tnc = malloc(sizeof(*tnc))) == NULL) {
         goto error_malloc_tnc;
     }
 
-    if ((tnc->buf = malloc(bufsz)) == NULL) {
+    if ((tnc->buf = malloc(PATTY_KISS_BUFSZ)) == NULL) {
         goto error_malloc_buf;
     }
 
     tnc->fd      = fd;
-    tnc->bufsz   = bufsz;
+    tnc->bufsz   = PATTY_KISS_BUFSZ;
     tnc->buflen  = 0;
     tnc->dropped = 0;
 
@@ -53,7 +53,7 @@ error_malloc_tnc:
     return NULL;
 }
 
-patty_kiss_tnc *patty_kiss_tnc_open(const char *device, size_t bufsz) {
+patty_kiss_tnc *patty_kiss_tnc_open(const char *device) {
     patty_kiss_tnc *tnc;
     int fd;
 
@@ -61,7 +61,7 @@ patty_kiss_tnc *patty_kiss_tnc_open(const char *device, size_t bufsz) {
         goto error_open;
     }
 
-    if ((tnc = patty_kiss_tnc_open_fd(fd, bufsz)) == NULL) {
+    if ((tnc = patty_kiss_tnc_open_fd(fd)) == NULL) {
         goto error_tnc_open_fd;
     }