diff --git a/cmUdpPort.c b/cmUdpPort.c
index 0048fbe..e981be6 100644
--- a/cmUdpPort.c
+++ b/cmUdpPort.c
@@ -18,6 +18,10 @@
 #define cmUdp_SYS_ERR (-1)
 #define cmUdp_NULL_SOCK (-1)
 
+#ifndef HOST_NAME_MAX
+#define HOST_NAME_MAX  _POSIX_HOST_NAME_MAX
+#endif
+
 enum
 {
   kIsConnectedUdpFl = 0x01,
@@ -99,6 +103,9 @@ cmUdpRC_t _cmUdpFree( cmUdp_t* p )
 cmUdpRC_t _cmUdpInitAddr( cmUdp_t* p, const char* addrStr, cmUdpPort_t portNumber, struct sockaddr_in* retAddrPtr )
 {
 	memset(retAddrPtr,0,sizeof(struct sockaddr_in));
+
+  if( portNumber == kInvalidUdpPortNumber )
+    return cmErrMsg(&p->err,kInvalidPortNumbUdpRC,"The port number %i cannot be used.",kInvalidUdpPortNumber);
 	
 	if( addrStr == NULL )
 		retAddrPtr->sin_addr.s_addr 	= htonl(INADDR_ANY);
diff --git a/cmUdpPort.h b/cmUdpPort.h
index 2d7cd48..6959f43 100644
--- a/cmUdpPort.h
+++ b/cmUdpPort.h
@@ -26,12 +26,13 @@ extern "C" {
     kRecvBufOverflowUdpRC,
     kBufTooSmallUdpRC,
     kHostNameFailUdpRC,
+    kInvalidPortNumbUdpRC,
     kTimeOutUdpRC
   };
 
-  typedef cmRC_t     cmUdpRC_t;
-  typedef cmHandle_t cmUdpH_t;
-  typedef u_short    cmUdpPort_t;
+  typedef cmRC_t         cmUdpRC_t;
+  typedef cmHandle_t     cmUdpH_t;
+  typedef unsigned short cmUdpPort_t;
 
   extern cmUdpH_t cmUdpNullHandle;
 
@@ -46,6 +47,12 @@ extern "C" {
     
   };
 
+  enum
+  {
+    // port 0 is reserved by and is therefore a convenient invalid port number
+    kInvalidUdpPortNumber = 0 
+  };
+
   cmUdpRC_t cmUdpAlloc( cmCtx_t* ctx, cmUdpH_t* hp );
   cmUdpRC_t cmUdpFree(  cmUdpH_t* hp );