diff --git a/asc2log.c b/asc2log.c
index fffce6e..e6f82d3 100644
--- a/asc2log.c
+++ b/asc2log.c
@@ -182,7 +182,7 @@ int main(int argc, char **argv)
 	int data[8];
 	int i, found, opt;
 
-	while ((opt = getopt(argc, argv, "I:O:v")) != -1) {
+	while ((opt = getopt(argc, argv, "I:O:v?")) != -1) {
 		switch (opt) {
 		case 'I':
 			infile = fopen(optarg, "r");
@@ -204,6 +204,11 @@ int main(int argc, char **argv)
 			verbose = 1;
 			break;
 
+		case '?':
+			print_usage(basename(argv[0]));
+			return 0;
+			break;
+
 		default:
 			fprintf(stderr, "Unknown option %c\n", opt);
 			print_usage(basename(argv[0]));
diff --git a/canplayer.c b/canplayer.c
index 074f6a9..1694622 100644
--- a/canplayer.c
+++ b/canplayer.c
@@ -245,7 +245,7 @@ int main(int argc, char **argv)
 	int eof, nbytes, i, j;
 	char *fret;
 
-	while ((opt = getopt(argc, argv, "I:l:tg:s:xv")) != -1) {
+	while ((opt = getopt(argc, argv, "I:l:tg:s:xv?")) != -1) {
 		switch (opt) {
 		case 'I':
 			infile = fopen(optarg, "r");
@@ -289,6 +289,7 @@ int main(int argc, char **argv)
 			verbose++;
 			break;
 
+		case '?':
 		default:
 			print_usage(basename(argv[0]));
 			return 1;
diff --git a/cansniffer.c b/cansniffer.c
index 649c39d..22d7e40 100644
--- a/cansniffer.c
+++ b/cansniffer.c
@@ -212,7 +212,7 @@ int main(int argc, char **argv)
 	for (i=0; i < 2048 ;i++) /* default: check all CAN-IDs */
 		do_set(i, ENABLE);
 
-	while ((opt = getopt(argc, argv, "m:v:r:t:h:l:qbBcf")) != -1) {
+	while ((opt = getopt(argc, argv, "m:v:r:t:h:l:qbBcf?")) != -1) {
 		switch (opt) {
 		case 'm':
 			sscanf(optarg, "%x", &mask);
diff --git a/isotpdump.c b/isotpdump.c
index c5c4de5..3ed02df 100644
--- a/isotpdump.c
+++ b/isotpdump.c
@@ -103,7 +103,7 @@ int main(int argc, char **argv)
 	last_tv.tv_sec  = 0;
 	last_tv.tv_usec = 0;
 
-	while ((opt = getopt(argc, argv, "s:d:ax:ct:")) != -1) {
+	while ((opt = getopt(argc, argv, "s:d:ax:ct:?")) != -1) {
 		switch (opt) {
 		case 's':
 			src = strtoul(optarg, (char **)NULL, 16);
@@ -144,10 +144,15 @@ int main(int argc, char **argv)
 			}
 			break;
 
+		case '?':
+			print_usage(basename(argv[0]));
+			exit(0);
+			break;
+
 		default:
 			fprintf(stderr, "Unknown option %c\n", opt);
 			print_usage(basename(argv[0]));
-			exit(0);
+			exit(1);
 			break;
 		}
 	}
diff --git a/isotprecv.c b/isotprecv.c
index 7b13cf2..9e37c86 100644
--- a/isotprecv.c
+++ b/isotprecv.c
@@ -94,7 +94,7 @@ int main(int argc, char **argv)
 
     addr.can_addr.tp.tx_id = addr.can_addr.tp.rx_id = NO_CAN_ID;
 
-    while ((opt = getopt(argc, argv, "s:d:x:p:P:b:m:w:l")) != -1) {
+    while ((opt = getopt(argc, argv, "s:d:x:p:P:b:m:w:l?")) != -1) {
 	    switch (opt) {
 	    case 's':
 		    addr.can_addr.tp.tx_id = strtoul(optarg, (char **)NULL, 16);
@@ -148,10 +148,15 @@ int main(int argc, char **argv)
 		    loop = 1;
 		    break;
 
+	    case '?':
+		    print_usage(basename(argv[0]));
+		    exit(0);
+		    break;
+
 	    default:
 		    fprintf(stderr, "Unknown option %c\n", opt);
 		    print_usage(basename(argv[0]));
-		    exit(0);
+		    exit(1);
 		    break;
 	    }
     }
@@ -160,7 +165,7 @@ int main(int argc, char **argv)
 	(addr.can_addr.tp.tx_id == NO_CAN_ID) ||
 	(addr.can_addr.tp.rx_id == NO_CAN_ID)) {
 	    print_usage(basename(argv[0]));
-	    exit(0);
+	    exit(1);
     }
   
     if ((s = socket(PF_CAN, SOCK_DGRAM, CAN_ISOTP)) < 0) {
diff --git a/isotpsend.c b/isotpsend.c
index 4320eaa..bcaa35b 100644
--- a/isotpsend.c
+++ b/isotpsend.c
@@ -88,7 +88,7 @@ int main(int argc, char **argv)
 
     addr.can_addr.tp.tx_id = addr.can_addr.tp.rx_id = NO_CAN_ID;
 
-    while ((opt = getopt(argc, argv, "s:d:x:p:P:t:")) != -1) {
+    while ((opt = getopt(argc, argv, "s:d:x:p:P:t:?")) != -1) {
 	    switch (opt) {
 	    case 's':
 		    addr.can_addr.tp.tx_id = strtoul(optarg, (char **)NULL, 16);
@@ -130,10 +130,15 @@ int main(int argc, char **argv)
 		    opts.frame_txtime = strtoul(optarg, (char **)NULL, 10);
 		    break;
 
+	    case '?':
+		    print_usage(basename(argv[0]));
+		    exit(0);
+		    break;
+
 	    default:
 		    fprintf(stderr, "Unknown option %c\n", opt);
 		    print_usage(basename(argv[0]));
-		    exit(0);
+		    exit(1);
 		    break;
 	    }
     }
@@ -142,7 +147,7 @@ int main(int argc, char **argv)
 	(addr.can_addr.tp.tx_id == NO_CAN_ID) ||
 	(addr.can_addr.tp.rx_id == NO_CAN_ID)) {
 	    print_usage(basename(argv[0]));
-	    exit(0);
+	    exit(1);
     }
   
     if ((s = socket(PF_CAN, SOCK_DGRAM, CAN_ISOTP)) < 0) {
diff --git a/isotpsniffer.c b/isotpsniffer.c
index 41fa438..f0b58be 100644
--- a/isotpsniffer.c
+++ b/isotpsniffer.c
@@ -193,7 +193,7 @@ int main(int argc, char **argv)
 	unsigned char buffer[4096];
 	int nbytes;
 
-	while ((opt = getopt(argc, argv, "s:d:x:h:ct:f:")) != -1) {
+	while ((opt = getopt(argc, argv, "s:d:x:h:ct:f:?")) != -1) {
 		switch (opt) {
 		case 's':
 			src = strtoul(optarg, (char **)NULL, 16);
@@ -234,17 +234,22 @@ int main(int argc, char **argv)
 			}
 			break;
 
+		case '?':
+			print_usage(basename(argv[0]));
+			exit(0);
+			break;
+
 		default:
 			fprintf(stderr, "Unknown option %c\n", opt);
 			print_usage(basename(argv[0]));
-			exit(0);
+			exit(1);
 			break;
 		}
 	}
 
 	if ((argc - optind) != 1 || src == NO_CAN_ID || dst == NO_CAN_ID) {
 		print_usage(basename(argv[0]));
-		exit(0);
+		exit(1);
 	}
   
 	if ((s = socket(PF_CAN, SOCK_DGRAM, CAN_ISOTP)) < 0) {
diff --git a/isotptun.c b/isotptun.c
index 5fca673..d40df87 100644
--- a/isotptun.c
+++ b/isotptun.c
@@ -111,7 +111,7 @@ int main(int argc, char **argv)
 
 	addr.can_addr.tp.tx_id = addr.can_addr.tp.rx_id = NO_CAN_ID;
 
-	while ((opt = getopt(argc, argv, "s:d:x:p:q:P:t:b:m:whv")) != -1) {
+	while ((opt = getopt(argc, argv, "s:d:x:p:q:P:t:b:m:whv?")) != -1) {
 		switch (opt) {
 		case 's':
 			addr.can_addr.tp.tx_id = strtoul(optarg, (char **)NULL, 16);
@@ -178,10 +178,15 @@ int main(int argc, char **argv)
 			verbose = 1;
 			break;
 
+		case '?':
+			print_usage(basename(argv[0]));
+			exit(0);
+			break;
+
 		default:
 			fprintf(stderr, "Unknown option %c\n", opt);
 			print_usage(basename(argv[0]));
-			exit(0);
+			exit(1);
 			break;
 		}
 	}
@@ -190,7 +195,7 @@ int main(int argc, char **argv)
 	    (addr.can_addr.tp.tx_id == NO_CAN_ID) ||
 	    (addr.can_addr.tp.rx_id == NO_CAN_ID)) {
 		print_usage(basename(argv[0]));
-		exit(0);
+		exit(1);
 	}
   
 	if ((s = socket(PF_CAN, SOCK_DGRAM, CAN_ISOTP)) < 0) {
diff --git a/log2asc.c b/log2asc.c
index 380990f..6a10f50 100644
--- a/log2asc.c
+++ b/log2asc.c
@@ -79,7 +79,7 @@ int main(int argc, char **argv)
 	FILE *outfile = stdout;
 	static int maxdev, devno, i, crlf, d4, opt;
 
-	while ((opt = getopt(argc, argv, "I:O:4n")) != -1) {
+	while ((opt = getopt(argc, argv, "I:O:4n?")) != -1) {
 		switch (opt) {
 		case 'I':
 			infile = fopen(optarg, "r");
@@ -105,6 +105,11 @@ int main(int argc, char **argv)
 			d4 = 1;
 			break;
 
+		case '?':
+			print_usage(basename(argv[0]));
+			return 0;
+			break;
+
 		default:
 			fprintf(stderr, "Unknown option %c\n", opt);
 			print_usage(basename(argv[0]));
diff --git a/slcan_attach.c b/slcan_attach.c
index 0ed7abe..ed6afc7 100644
--- a/slcan_attach.c
+++ b/slcan_attach.c
@@ -86,7 +86,7 @@ int main(int argc, char **argv)
 	char *tty;
 	int opt;
 
-	while ((opt = getopt(argc, argv, "l:dwocs:b:")) != -1) {
+	while ((opt = getopt(argc, argv, "l:dwocs:b:?")) != -1) {
 		switch (opt) {
 		case 'l':
 			fprintf(stderr, "Ignored option '-l'\n");
@@ -120,6 +120,7 @@ int main(int argc, char **argv)
 				print_usage(argv[0]);
 			break;
 
+		case '?':
 		default:
 			print_usage(argv[0]);
 			break;