diff --git a/README.md b/README.md
index 349314a..4d339e3 100644
--- a/README.md
+++ b/README.md
@@ -119,7 +119,7 @@ Options:
   -i               Disable ionospheric delay for spacecraft scenario
   -v               Show details about simulated channels
   -n <port>        Use TCP connection to Gnuradio TCP-Source for realtime simulation.
-  -w               Connect with map server(/mapserver/mapper.py) by udp on port 5678.
+  -w <port>        Connect with map server(/mapserver/mapper.py) by UDP (default port 5678).
 ```
 
 The user motion can be specified in either dynamic or static mode:
diff --git a/gpssim.c b/gpssim.c
index b32bb16..d8df09a 100644
--- a/gpssim.c
+++ b/gpssim.c
@@ -1667,7 +1667,7 @@ void usage(void)
 		"  -i               Disable ionospheric delay for spacecraft scenario\n"
 		"  -v               Show details about simulated channels\n"
 		"  -n <port>        Use TCP connect to Gnuradio TCP-Source for\n realtime simulation.\n"
-		"-w               Connect with map server(/mapserver/mapper.py) by udp on port 5678.\n",
+		"  -w <port>        Connect with map server(/mapserver/mapper.py) by UDP (default port 5678).\n",
 		(double)((USER_MOTION_SIZE)/10.0),(int)STATIC_MAX_DURATION);
 
 	return;
@@ -1740,6 +1740,7 @@ int main(int argc, char *argv[])
 	int webflag=0;
 	int sockc=0;
 	short port=1234;
+    short mapport=5678;
 
 	////////////////////////////////////////////////////////////
 	// Read options
@@ -1862,6 +1863,7 @@ int main(int argc, char *argv[])
 			usesocket=true;
 			break;
 		case  'w':
+            sscanf(optarg,"%hd",&mapport);
 			staticLocationMode = TRUE;
 			webflag=1;
 			break;
@@ -1872,7 +1874,7 @@ int main(int argc, char *argv[])
 	}
 	if(webflag==1){
 		pthread_t th;
-		pthread_create(&th,NULL,(void *)threadrecv,NULL);
+		pthread_create(&th,NULL,(void *)threadrecv,(void *)&mapport);
 	}	
 	if(usesocket==1)
 		sockc=sockinit(port);
diff --git a/socket.c b/socket.c
index 3076989..8152b5f 100644
--- a/socket.c
+++ b/socket.c
@@ -62,10 +62,10 @@ int udprecv(int s,void *dataa,int siz){
 
 double llhr[3]={39.68,139,76};
 
-void threadrecv(){
+void threadrecv(void *p){
 	printf("listing\n");
-	short p=5678;
-	int s=udpinit(p);
+	short port=*(short*)p;
+	int s=udpinit(port);
 	while(1){
 		udprecv(s,llhr,3*sizeof(double));
 		//printf("%lf%lf%lf\n",llhr[0],llhr[1],llhr[2]);