diff --git a/dmd2/mars.c b/dmd2/mars.c
index 125f7c38..d895297f 100644
--- a/dmd2/mars.c
+++ b/dmd2/mars.c
@@ -16,7 +16,7 @@
 #include <string>
 #include <cstdarg>
 
-#if linux || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun
+#if __linux__ || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun
 #include <errno.h>
 #endif
 
@@ -517,7 +517,7 @@ int tryMain(size_t argc, char *argv[])
 
 #if _WIN32
     inifilename = inifile(argv[0], "sc.ini", "Environment");
-#elif linux || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun
+#elif __linux__ || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun
     inifilename = inifile(argv[0], "dmd.conf", "Environment");
 #else
 #error "fix this"
@@ -917,7 +917,7 @@ Language changes listed by -transition=id:\n\
                 browse("http://dlang.org/dmd-windows.html");
 #endif
 #endif
-#if linux
+#if __linux__
 #if DMDV1
                 browse("http://www.digitalmars.com/d/1.0/dmd-linux.html");
 #else
diff --git a/dmd2/root/async.c b/dmd2/root/async.c
index 92767c8e..d68237d1 100644
--- a/dmd2/root/async.c
+++ b/dmd2/root/async.c
@@ -119,7 +119,7 @@ unsigned __stdcall startthread(void *p)
     return EXIT_SUCCESS;                // if skidding
 }
 
-#elif linux  // Posix
+#elif __linux__  // Posix
 
 #include <errno.h>
 #include <pthread.h>
diff --git a/dmd2/root/man.c b/dmd2/root/man.c
index f49d60b4..462ef92a 100644
--- a/dmd2/root/man.c
+++ b/dmd2/root/man.c
@@ -26,7 +26,7 @@ void browse(const char *url)
 
 #endif
 
-#if linux || __FreeBSD__ || __OpenBSD__ || __sun
+#if __linux__ || __FreeBSD__ || __OpenBSD__ || __sun
 
 #include        <sys/types.h>
 #include        <sys/wait.h>
diff --git a/dmd2/root/port.c b/dmd2/root/port.c
index 4422809a..044f2444 100644
--- a/dmd2/root/port.c
+++ b/dmd2/root/port.c
@@ -542,10 +542,10 @@ longdouble Port::strtold(const char *p, char **endp)
 
 #endif
 
-#if linux || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __HAIKU__
+#if __linux__ || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __HAIKU__
 
 #include <math.h>
-#if linux
+#if __linux__
 #include <bits/nan.h>
 #include <bits/mathdef.h>
 #endif
diff --git a/dmd2/root/rmem.c b/dmd2/root/rmem.c
index ce6b3e0d..d4e9d265 100644
--- a/dmd2/root/rmem.c
+++ b/dmd2/root/rmem.c
@@ -11,7 +11,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#if linux || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun
+#if __linux__ || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun
 #include "../root/rmem.h"
 #else
 #include "rmem.h"
diff --git a/dmd2/root/root.c b/dmd2/root/root.c
index 900a3e65..5e172897 100644
--- a/dmd2/root/root.c
+++ b/dmd2/root/root.c
@@ -8,7 +8,7 @@
 // See the included readme.txt for details.
 
 #ifndef POSIX
-#define POSIX (linux || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun)
+#define POSIX (__linux__ || __APPLE__ || __FreeBSD__ || __OpenBSD__ || __sun)
 #endif
 
 #include <stdio.h>
@@ -878,11 +878,11 @@ void FileName::ensurePathToNameExists(const char *name)
  */
 const char *FileName::canonicalName(const char *name)
 {
-#if linux
+#if __linux__
     // Lovely glibc extension to do it for us
     return canonicalize_file_name(name);
 #elif POSIX
-  #if _POSIX_VERSION >= 200809L || defined (linux)
+  #if _POSIX_VERSION >= 200809L || defined (__linux__)
     // NULL destination buffer is allowed and preferred
     return realpath(name, NULL);
   #else