diff --git a/src/AudioStream.c b/src/AudioStream.c
index 4cd18f1..b4b2a9c 100644
--- a/src/AudioStream.c
+++ b/src/AudioStream.c
@@ -45,6 +45,8 @@ static void AudioPingThreadProc(void* context) {
     char pingData[] = { 0x50, 0x49, 0x4E, 0x47 };
     LC_SOCKADDR saddr;
 
+    LC_ASSERT(AudioPortNumber != 0);
+
     memcpy(&saddr, &RemoteAddr, sizeof(saddr));
     SET_PORT(&saddr, AudioPortNumber);
 
@@ -94,11 +96,12 @@ int initializeAudioStream(void) {
     return 0;
 }
 
-// This is called when the RTSP DESCRIBE message is parsed and the audio port
+// This is called when the RTSP SETUP message is parsed and the audio port
 // number is parsed out of it. Alternatively, it's also called if parsing fails
 // and will use the well known audio port instead.
 int notifyAudioPortNegotiationComplete(void) {
     LC_ASSERT(!pingThreadStarted);
+    LC_ASSERT(AudioPortNumber != 0);
 
     // We may receive audio before our threads are started, but that's okay. We'll
     // drop the first 1 second of audio packets to catch up with the backlog.
diff --git a/src/Connection.c b/src/Connection.c
index e0213c1..430a543 100644
--- a/src/Connection.c
+++ b/src/Connection.c
@@ -238,11 +238,10 @@ int LiStartConnection(PSERVER_INFORMATION serverInfo, PSTREAM_CONFIGURATION stre
     OriginalVideoBitrate = streamConfig->bitrate;
     RemoteAddrString = strdup(serverInfo->address);
 
-    // Initialize port numbers to defaults. The values in RTSP SETUP (if valid)
-    // will override these to allow dynamic port selection.
-    VideoPortNumber = 47998;
-    ControlPortNumber = 47999;
-    AudioPortNumber = 48000;
+    // The values in RTSP SETUP will be used to populate these.
+    VideoPortNumber = 0;
+    ControlPortNumber = 0;
+    AudioPortNumber = 0;
 
     // Parse RTSP port number from RTSP session URL
     if (!parseRtspPortNumberFromUrl(serverInfo->rtspSessionUrl, &RtspPortNumber)) {
diff --git a/src/ControlStream.c b/src/ControlStream.c
index 02fe462..18055ad 100644
--- a/src/ControlStream.c
+++ b/src/ControlStream.c
@@ -1142,6 +1142,8 @@ int startControlStream(void) {
         ENetAddress address;
         ENetEvent event;
         
+        LC_ASSERT(ControlPortNumber != 0);
+
         enet_address_set_address(&address, (struct sockaddr *)&RemoteAddr, RemoteAddrLen);
         enet_address_set_port(&address, ControlPortNumber);
 
@@ -1183,6 +1185,7 @@ int startControlStream(void) {
     }
     else {
         // NB: Do NOT use ControlPortNumber here. 47995 is correct for these old versions.
+        LC_ASSERT(ControlPortNumber == 0);
         ctlSock = connectTcpSocket(&RemoteAddr, RemoteAddrLen,
             47995, CONTROL_STREAM_TIMEOUT_SEC);
         if (ctlSock == INVALID_SOCKET) {
diff --git a/src/RtspConnection.c b/src/RtspConnection.c
index 3e36fcc..4083286 100644
--- a/src/RtspConnection.c
+++ b/src/RtspConnection.c
@@ -672,6 +672,8 @@ int performRtspHandshake(void) {
         strcpy(urlAddr, "0.0.0.0");
     }
 
+    LC_ASSERT(RtspPortNumber != 0);
+
     // Initialize global state
     useEnet = (AppVersionQuad[0] >= 5) && (AppVersionQuad[0] <= 7) && (AppVersionQuad[2] < 404);
     sprintf(rtspTargetUrl, "rtsp%s://%s:%u", useEnet ? "ru" : "", urlAddr, RtspPortNumber);
@@ -833,7 +835,11 @@ int performRtspHandshake(void) {
         }
 
         // Parse the audio port out of the RTSP SETUP response
+        LC_ASSERT(AudioPortNumber == 0);
         if (!parseServerPortFromTransport(&response, &AudioPortNumber)) {
+            // Use the well known port if parsing fails
+            AudioPortNumber = 48000;
+
             Limelog("Audio port: %u (RTSP parsing failed)\n", AudioPortNumber);
         }
         else {
@@ -890,7 +896,11 @@ int performRtspHandshake(void) {
         }
 
         // Parse the video port out of the RTSP SETUP response
+        LC_ASSERT(VideoPortNumber == 0);
         if (!parseServerPortFromTransport(&response, &VideoPortNumber)) {
+            // Use the well known port if parsing fails
+            VideoPortNumber = 47998;
+
             Limelog("Video port: %u (RTSP parsing failed)\n", VideoPortNumber);
         }
         else {
@@ -920,7 +930,11 @@ int performRtspHandshake(void) {
         }
 
         // Parse the control port out of the RTSP SETUP response
+        LC_ASSERT(ControlPortNumber == 0);
         if (!parseServerPortFromTransport(&response, &ControlPortNumber)) {
+            // Use the well known port if parsing fails
+            ControlPortNumber = 47999;
+
             Limelog("Control port: %u (RTSP parsing failed)\n", ControlPortNumber);
         }
         else {
diff --git a/src/SdpGenerator.c b/src/SdpGenerator.c
index b0f1190..e9c301a 100644
--- a/src/SdpGenerator.c
+++ b/src/SdpGenerator.c
@@ -133,6 +133,7 @@ static int addGen4Options(PSDP_OPTION* head, char* addrStr) {
     char payloadStr[92];
     int err = 0;
 
+    LC_ASSERT(RtspPortNumber != 0);
     sprintf(payloadStr, "rtsp://%s:%u", addrStr, RtspPortNumber);
     err |= addAttributeString(head, "x-nv-general.serverAddress", payloadStr);
 
@@ -461,6 +462,7 @@ static int fillSdpHeader(char* buffer, int rtspClientVersion, char*urlSafeAddr)
 
 // Populate the SDP tail with required information
 static int fillSdpTail(char* buffer) {
+    LC_ASSERT(VideoPortNumber != 0);
     return sprintf(buffer,
         "t=0 0\r\n"
         "m=video %d  \r\n",
diff --git a/src/VideoStream.c b/src/VideoStream.c
index 8244ad0..eac29a3 100644
--- a/src/VideoStream.c
+++ b/src/VideoStream.c
@@ -46,6 +46,8 @@ static void VideoPingThreadProc(void* context) {
     char pingData[] = { 0x50, 0x49, 0x4E, 0x47 };
     LC_SOCKADDR saddr;
 
+    LC_ASSERT(VideoPortNumber != 0);
+
     memcpy(&saddr, &RemoteAddr, sizeof(saddr));
     SET_PORT(&saddr, VideoPortNumber);