diff --git a/log2asc.c b/log2asc.c
index ad9fe8e..9180144 100644
--- a/log2asc.c
+++ b/log2asc.c
@@ -67,6 +67,7 @@ void print_usage(char *prg)
 	fprintf(stderr, "         -O <outfile>  (default stdout)\n");
 	fprintf(stderr, "         -4  (reduce decimal place to 4 digits)\n");
 	fprintf(stderr, "         -n  (set newline to cr/lf - default lf)\n");
+	fprintf(stderr, "         -f  (use CANFD format also for Classic CAN)\n");
 }
 
 void can_asc(struct canfd_frame *cf, int devno, FILE *outfile)
@@ -95,11 +96,18 @@ void can_asc(struct canfd_frame *cf, int devno, FILE *outfile)
 	}
 }
 
-void canfd_asc(struct canfd_frame *cf, int devno, FILE *outfile)
+void canfd_asc(struct canfd_frame *cf, int devno, int mtu, FILE *outfile)
 {
 	int i;
 	char id[10];
-	unsigned int flags;
+	unsigned int flags = 0;
+	unsigned int dlen = cf->len;
+
+	/* relevant flags in Flags field */
+#define ASC_F_RTR 0x00000010
+#define ASC_F_FDF 0x00001000
+#define ASC_F_BRS 0x00002000
+#define ASC_F_ESI 0x00004000
 
 	fprintf(outfile, "CANFD %3d Rx ", devno); /* 3 column channel number right aligned */
 
@@ -108,23 +116,27 @@ void canfd_asc(struct canfd_frame *cf, int devno, FILE *outfile)
 	fprintf(outfile, "%11s                                  ", id);
 	fprintf(outfile, "%c ", (cf->flags & CANFD_BRS)?'1':'0');
 	fprintf(outfile, "%c ", (cf->flags & CANFD_ESI)?'1':'0');
-	fprintf(outfile, "%x ", can_len2dlc(cf->len));
-	fprintf(outfile, "%2d", cf->len);
+	fprintf(outfile, "%x ", can_len2dlc(dlen));
 
-	for (i = 0; i < cf->len; i++) {
-		fprintf(outfile, " %02X", cf->data[i]);
+	if (mtu == CAN_MTU) {
+		if (cf->can_id & CAN_RTR_FLAG) {
+			/* no data length but dlc for RTR frames */
+			dlen = 0;
+			flags = ASC_F_RTR;
+		}
+	} else {
+		flags = ASC_F_FDF;
+		if (cf->flags & CANFD_BRS)
+			flags |= ASC_F_BRS;
+		if (cf->flags & CANFD_ESI)
+			flags |= ASC_F_ESI;
 	}
 
-	/* relevant flags in Flags field */
-#define ASC_F_FDF 0x00001000
-#define ASC_F_BRS 0x00002000
-#define ASC_F_ESI 0x00004000
+	fprintf(outfile, "%2d", dlen);
 
-	flags = ASC_F_FDF;
-	if (cf->flags & CANFD_BRS)
-		flags |= ASC_F_BRS;
-	if (cf->flags & CANFD_ESI)
-		flags |= ASC_F_ESI;
+	for (i = 0; i < dlen; i++) {
+		fprintf(outfile, " %02X", cf->data[i]);
+	}
 
 	fprintf(outfile, " %8d %4d %8X 0 0 0 0 0", 130000, 130, flags);
 }
@@ -137,9 +149,9 @@ int main(int argc, char **argv)
 	static struct timeval tv, start_tv;
 	FILE *infile = stdin;
 	FILE *outfile = stdout;
-	static int maxdev, devno, i, crlf, d4, opt, mtu;
+	static int maxdev, devno, i, crlf, fdfmt, d4, opt, mtu;
 
-	while ((opt = getopt(argc, argv, "I:O:4n?")) != -1) {
+	while ((opt = getopt(argc, argv, "I:O:4nf?")) != -1) {
 		switch (opt) {
 		case 'I':
 			infile = fopen(optarg, "r");
@@ -161,6 +173,10 @@ int main(int argc, char **argv)
 			crlf = 1;
 			break;
 
+		case 'f':
+			fdfmt = 1;
+			break;
+
 		case '4':
 			d4 = 1;
 			break;
@@ -242,10 +258,10 @@ int main(int argc, char **argv)
 			else
 				fprintf(outfile, "%4ld.%06ld ", tv.tv_sec, tv.tv_usec);
 
-			if (mtu == CAN_MTU)
+			if ((mtu == CAN_MTU) && (fdfmt == 0))
 				can_asc(&cf, devno, outfile);
 			else
-				canfd_asc(&cf, devno, outfile);
+				canfd_asc(&cf, devno, mtu, outfile);
 
 			if (crlf)
 				fprintf(outfile, "\r");