diff --git a/shoot.c b/shoot.c
index 2e5d5b4..1d89fe4 100644
--- a/shoot.c
+++ b/shoot.c
@@ -183,7 +183,7 @@ void trace_reply()
 			printf("(%.3f ms) ", deltaT(&(timers.sendtime), &(timers.recvtime)));
 			print_message_line(rec);
 		}
-		delays.retryAfter = SIP_T2;
+		delays.retryAfter = timer_t2;
 		cdata.dontsend=1;
 		return;
 	}
@@ -235,10 +235,10 @@ void handle_default()
 					" waiting for a final response\n");
 		}
 		if (inv_trans) {
-			delays.retryAfter = inv_final;
+			delays.retryAfter = timer_final;
 		}
 		else {
-			delays.retryAfter = SIP_T2;
+			delays.retryAfter = timer_t2;
 		}
 		cdata.dontsend = 1;
 		return;
@@ -273,7 +273,7 @@ void handle_default()
 			else {
 				counters.run++;
 				new_transaction(req);
-				delays.retryAfter = SIP_T1;
+				delays.retryAfter = timer_t1;
 			}
 		}
 		if (timing == 0) {
@@ -340,10 +340,10 @@ void handle_usrloc()
 			printf("ignoring provisional response\n\n");
 		}
 		if (inv_trans) {
-			delays.retryAfter = inv_final;
+			delays.retryAfter = timer_final;
 		}
 		else {
-			delays.retryAfter = SIP_T2;
+			delays.retryAfter = timer_t2;
 		}
 		cdata.dontsend = 1;
 	}
@@ -794,10 +794,10 @@ void shoot(char *buf, int buff_size)
 
 	/* delays.retryAfter = DEFAULT_TIMEOUT; */
 	if (transport == SIP_UDP_TRANSPORT) {
-		delays.retryAfter = SIP_T1;
+		delays.retryAfter = timer_t1;
 	}
 	else {
-		delays.retryAfter = inv_final;
+		delays.retryAfter = timer_final;
 	}
 	inv_trans = 0;
 	cseq_counter = 1;
@@ -1009,7 +1009,7 @@ void shoot(char *buf, int buff_size)
 							}
 							counters.run++;
 							new_transaction(req);
-							delays.retryAfter = SIP_T1;
+							delays.retryAfter = timer_t1;
 							continue;
 						}
 						fprintf(stderr, "%s\nerror: received 40[17] but cannot "
diff --git a/sipsak.1 b/sipsak.1
index d65ba0e..7c359cb 100644
--- a/sipsak.1
+++ b/sipsak.1
@@ -526,6 +526,12 @@ per cent of the bindings will be removed, is determined by the
 USRLOC_REMOVE_PERCENT define within the code (set it before compilation).
 Multiple removing of bindings is possible, and cannot be prevented.
 
+.IP "-Z, --timer-t1"
+Sets the amount of milliseconds for the SIP timer T1. It determines the
+length of the gaps between two retransmissions of a request on a unreliable
+transport. Default value is 500 if not changed via the configure option
+--enable-timeout.
+
 .SH RETURN VALUES
 The return value 0 means that a 200 was received. 1 means something else 
 then 1xx or 2xx was received.
diff --git a/sipsak.c b/sipsak.c
index 81fafa4..ba7ca6a 100644
--- a/sipsak.c
+++ b/sipsak.c
@@ -153,9 +153,11 @@ void print_long_help() {
 		"  --from=SIPURI              use the given uri as From in MESSAGE\n"
 		"  --timeout-factor=NUMBER    timeout multiplier for INVITE transactions\n"
 		"                             on non-reliable transports (default: 64)\n"
+		"  --timer-t1=NUMBER          timeout T1 in ms (default: %i)\n"
 		"  --transport=STRING         specify transport to be used\n"
 		"  --headers=STRING           adds additional headers to the request\n"
 		"  --authhash=STRING          ha1 hash for authentication instead of password\n"
+		, DEFAULT_TIMEOUT
 		);
 	exit_code(0);
 }
@@ -225,9 +227,11 @@ void print_help() {
 		"  -c SIPURI         use the given uri as From in MESSAGE\n"
 		"  -D NUMBER         timeout multiplier for INVITE transactions\n"
 		"                    on non-reliable transports (default: 64)\n"
+		"  -Z NUMBER         timeout T1 in ms (default: %i)\n"
 		"  -E STRING         specify transport to be used\n"
 		"  -j STRING         adds additional headers to the request\n"
 		"  -J STRING         ha1 hash for authentication instead of password\n"
+		, DEFAULT_TIMEOUT
 		);
 		exit_code(0);
 }
@@ -288,6 +292,7 @@ int main(int argc, char *argv[])
 		{"symmetric", 0, 0, 'S'},
 		{"from", 1, 0, 'c'},
 		{"timeout-factor", 1, 0, 'D'},
+		{"timer-t1", 1, 0, 'Z'},
 		{"transport", 1, 0, 'E'},
 		{"headers", 1, 0, 'j'},
 		{"authhash", 1, 0, 'J'},
@@ -316,7 +321,9 @@ int main(int argc, char *argv[])
 	transport=tsp = 0;
 	rport = port = 0;
 	expires_t = USRLOC_EXP_DEF;
-	inv_final = 64 * SIP_T1;
+	timer_t1 = SIP_T1;
+	timer_t2 = 8;
+	timer_final = 64;
 	memset(buff, 0, BUFSIZE);
 	memset(fqdn, 0, FQDN_SIZE);
 #ifdef WITH_TLS_TRANSP
@@ -338,9 +345,9 @@ int main(int argc, char *argv[])
 
 	/* lots of command line switches to handle*/
 #ifdef HAVE_GETOPT_LONG
-	while ((c=getopt_long(argc, argv, "a:A:b:B:c:C:dD:e:E:f:Fg:GhH:iIj:J:l:Lm:MnNo:O:p:P:q:r:Rs:St:Tu:UvVwW:x:Xz:", l_opts, &option_index)) != EOF){
+	while ((c=getopt_long(argc, argv, "a:A:b:B:c:C:dD:e:E:f:Fg:GhH:iIj:J:l:Lm:MnNo:O:p:P:q:r:Rs:St:Tu:UvVwW:x:Xz:Z:", l_opts, &option_index)) != EOF){
 #else
-	while ((c=getopt(argc, argv, "a:A:b:B:c:C:dD:e:E:f:Fg:GhH:iIj:J:l:Lm:MnNo:O:p:P:q:r:Rs:St:Tu:UvVwW:x:z:")) != EOF){
+	while ((c=getopt(argc, argv, "a:A:b:B:c:C:dD:e:E:f:Fg:GhH:iIj:J:l:Lm:MnNo:O:p:P:q:r:Rs:St:Tu:UvVwW:x:z:Z:")) != EOF){
 #endif
 		switch(c){
 			case 'a':
@@ -426,7 +433,11 @@ int main(int argc, char *argv[])
 				redirects=0;
 				break;
 			case 'D':
-				inv_final = str_to_int(0, optarg) * SIP_T1;
+				timer_final = str_to_int(0, optarg);
+				if (timer_final <= 0) {
+					fprintf(stderr, "error: option D has to be above 0\n");
+					exit_code(2);
+				}
 				break;
 			case 'e':
 				nameend=str_to_int(0, optarg);
@@ -771,6 +782,13 @@ int main(int argc, char *argv[])
 					exit_code(2);
 				}
 				break;
+			case 'Z':
+				timer_t1 = str_to_int(0, optarg);
+				if (timer_t1 <= 0) {
+					fprintf(stderr, "error: Z option must be above 0\n");
+					exit_code(2);
+				}
+				break;
 			default:
 				fprintf(stderr, "error: unknown parameter %c\n", c);
 				exit_code(2);
@@ -789,6 +807,9 @@ int main(int argc, char *argv[])
 		transport = SIP_UDP_TRANSPORT;
 	}
 
+	timer_t2 = timer_t2 * timer_t1;
+	timer_final = timer_final * timer_t1;
+
 	/* replace LF with CRLF if we read from a file */
 	if ((file_b) && (fix_crlf)) {
 		insert_cr(buff);
diff --git a/sipsak.h b/sipsak.h
index 9c94a8f..ae49823 100644
--- a/sipsak.h
+++ b/sipsak.h
@@ -325,7 +325,8 @@ int sleep_ms, processes, cseq_counter;
 int verbose, nameend, namebeg, expires_t, flood, warning_ext, invite, message;
 int maxforw, lport, rport, randtrash, trashchar, numeric, symmetric;
 int file_b, uri_b, trace, via_ins, usrloc, redirects, rand_rem, replace_b;
-int empty_contact, nagios_warn, fix_crlf, timing, outbound_proxy, inv_final;
+int empty_contact, nagios_warn, fix_crlf, timing, outbound_proxy;
+int timer_t1, timer_t2, timer_final;
 char *username, *domainname, *password, *replace_str, *hostname, *contact_uri;
 char *mes_body, *con_dis, *auth_username, *from_uri, *headers, *authhash;
 char fqdn[FQDN_SIZE];
diff --git a/transport.c b/transport.c
index 5c3c86c..734ee2a 100644
--- a/transport.c
+++ b/transport.c
@@ -766,7 +766,7 @@ int check_for_message(char *recv, int size, struct sipsak_con_data *cd,
 	if (count->send_counter==1) {
 		memcpy(&(srt->firstsendt), &(srt->sendtime), sizeof(struct timeval));
 	}
-	if (sd->retryAfter == SIP_T1) {
+	if (sd->retryAfter == timer_t1) {
 		memcpy(&(srt->starttime), &(srt->sendtime), sizeof(struct timeval));
 	}
 	if (ret == 0)
@@ -805,7 +805,7 @@ int check_for_message(char *recv, int size, struct sipsak_con_data *cd,
 			}
 		}
 		senddiff = deltaT(&(srt->starttime), &(srt->recvtime));
-		if (senddiff > (float)inv_final) {
+		if (senddiff > (float)timer_final) {
 			if (timing == 0) {
 				if (verbose>0)
 					printf("*** giving up, no final response after %.3f ms\n", senddiff);
@@ -817,7 +817,7 @@ int check_for_message(char *recv, int size, struct sipsak_con_data *cd,
 				sd->all_delay += senddiff;
 				sd->big_delay = senddiff;
 				new_transaction(req);
-				sd->retryAfter = SIP_T1;
+				sd->retryAfter = timer_t1;
 				if (timing == 0) {
 					printf("%.3f/%.3f/%.3f ms\n", sd->small_delay, sd->all_delay / count->run, sd->big_delay);
 					exit_code(3);
@@ -826,11 +826,11 @@ int check_for_message(char *recv, int size, struct sipsak_con_data *cd,
 		}
 		else {
 			/* set retry time according to RFC3261 */
-			if ((inv_trans) || (sd->retryAfter *2 < SIP_T2)) {
+			if ((inv_trans) || (sd->retryAfter *2 < timer_t2)) {
 				sd->retryAfter = sd->retryAfter * 2;
 			}
 			else {
-				sd->retryAfter = SIP_T2;
+				sd->retryAfter = timer_t2;
 			}
 		}
 		(count->retrans_s_c)++;
@@ -1070,7 +1070,7 @@ int recv_message(char *buf, int size, int inv_trans,
 			printf(":\n");
 #endif // HAVE_INET_NTOP
 		if (!inv_trans && ret > 0 && (regexec(&(reg->proexp), buf, 0, 0, 0) != REG_NOERROR)) {
-			sd->retryAfter = SIP_T1;
+			sd->retryAfter = timer_t1;
 		}
 	}
 	else {