diff --git a/src/iec61850/inc/iec61850_server.h b/src/iec61850/inc/iec61850_server.h
index 9080a6b1..4672c718 100644
--- a/src/iec61850/inc/iec61850_server.h
+++ b/src/iec61850/inc/iec61850_server.h
@@ -113,7 +113,7 @@ IedServer_setFilestoreBasepath(IedServer self, const char* basepath);
  * \brief Start handling client connections
  *
  * \param self the instance of IedServer to operate on.
- * \param tcpPort the TCP port the server is listening
+ * \param tcpPort the TCP port the server is listening (-1 for using the default MMS or secure MMS port)
  */
 void
 IedServer_start(IedServer self, int tcpPort);
@@ -134,7 +134,7 @@ IedServer_stop(IedServer self);
  * be called periodically.
  *
  * \param self the instance of IedServer to operate on.
- * \param tcpPort the TCP port the server is listening
+ * \param tcpPort the TCP port the server is listening (-1 for using the default MMS or secure MMS port)
  */
 void
 IedServer_startThreadless(IedServer self, int tcpPort);
diff --git a/src/mms/iso_mms/server/mms_server.c b/src/mms/iso_mms/server/mms_server.c
index 577590b9..5781812c 100644
--- a/src/mms/iso_mms/server/mms_server.c
+++ b/src/mms/iso_mms/server/mms_server.c
@@ -394,7 +394,10 @@ void
 MmsServer_startListeningThreadless(MmsServer self, int tcpPort)
 {
     IsoServer_setConnectionHandler(self->isoServer, isoConnectionIndicationHandler, (void*) self);
-    IsoServer_setTcpPort(self->isoServer, tcpPort);
+
+    if (tcpPort != -1)
+        IsoServer_setTcpPort(self->isoServer, tcpPort);
+
     IsoServer_startListeningThreadless(self->isoServer);
 }