diff --git a/mdstcpip/udt4/src/channel.cpp b/mdstcpip/udt4/src/channel.cpp
index e408471b6e..51d15f51e4 100644
--- a/mdstcpip/udt4/src/channel.cpp
+++ b/mdstcpip/udt4/src/channel.cpp
@@ -124,7 +124,7 @@ void CChannel::open(UDPSOCKET udpsock) {
 }
 
 void CChannel::setUDPSockOpt() {
-#if defined(BSD) || defined(OSX)
+#if defined(BSD) || defined(__APPLE__)
   // BSD system will fail setsockopt if the requested buffer size exceeds system
   // maximum value
   int maxsize = 64000;
@@ -148,7 +148,7 @@ void CChannel::setUDPSockOpt() {
 
   timeval tv;
   tv.tv_sec = 0;
-#if defined(BSD) || defined(OSX)
+#if defined(BSD) || defined(__APPLE__)
   // Known BSD bug as the day I wrote this code.
   // A small time out value will cause the socket to block forever.
   tv.tv_usec = 10000;
diff --git a/mdstcpip/udt4/src/common.cpp b/mdstcpip/udt4/src/common.cpp
index 77841d745c..3daa18a444 100644
--- a/mdstcpip/udt4/src/common.cpp
+++ b/mdstcpip/udt4/src/common.cpp
@@ -42,7 +42,7 @@ written by
 #include <cstring>
 #include <cerrno>
 #include <unistd.h>
-#ifdef OSX
+#ifdef __APPLE__
 #include <mach/mach_time.h>
 #endif
 #else
@@ -115,7 +115,7 @@ void CTimer::rdtsc(uint64_t &x) {
   // SetThreadAffinityMask(hCurThread, dwOldMask);
   if (!ret)
     x = getTime() * s_ullCPUFrequency;
-#elif defined(OSX)
+#elif defined(__APPLE__)
   x = mach_absolute_time();
 #else
   // use system call to read time clock for other archs
@@ -142,7 +142,7 @@ uint64_t CTimer::readCPUFrequency() {
   int64_t ccf;
   if (QueryPerformanceFrequency((LARGE_INTEGER *)&ccf))
     frequency = ccf / 1000000;
-#elif defined(OSX)
+#elif defined(__APPLE__)
   mach_timebase_info_data_t info;
   mach_timebase_info(&info);
   frequency = info.denom * 1000ULL / info.numer;