diff --git a/opal/class/opal_object.h b/opal/class/opal_object.h
index 00132141d2..766bec3ae4 100644
--- a/opal/class/opal_object.h
+++ b/opal/class/opal_object.h
@@ -115,7 +115,9 @@
 #define OPAL_OBJECT_H
 
 #include <assert.h>
+#ifdef HAVE_STDLIB_H
 #include <stdlib.h>
+#endif  /* HAVE_STDLIB_H */
 
 #include "include/sys/atomic.h"
 
diff --git a/opal/mca/base/mca_base_component_find.c b/opal/mca/base/mca_base_component_find.c
index cafdf58a35..f6b17a898a 100644
--- a/opal/mca/base/mca_base_component_find.c
+++ b/opal/mca/base/mca_base_component_find.c
@@ -215,7 +215,7 @@ static void find_dyn_components(const char *path, const char *type_name,
   dir = path_to_use;
   if (NULL != dir) {
     do {
-#ifdef WIN32
+#ifdef __WINDOWS__
       end = strchr(dir, ';');
 #else
       end = strchr(dir, ':');
diff --git a/opal/mca/base/mca_base_open.c b/opal/mca/base/mca_base_open.c
index 99a58113b2..b8a55786a1 100644
--- a/opal/mca/base/mca_base_open.c
+++ b/opal/mca/base/mca_base_open.c
@@ -69,7 +69,7 @@ int mca_base_open(void)
 
   /* Register some params */
 
-#ifdef WIN32
+#ifdef __WINDOWS__
   asprintf(&value, "%s;~/.openmpi/components", OMPI_PKGLIBDIR);
 #else
   asprintf(&value, "%s:~/.openmpi/components", OMPI_PKGLIBDIR);
@@ -121,7 +121,7 @@ static void set_defaults(opal_output_stream_t *lds)
     /* Load up defaults */
 
     OBJ_CONSTRUCT(lds, opal_output_stream_t);
-#ifndef WIN32
+#ifndef __WINDOWS__
     lds->lds_syslog_priority = LOG_INFO;
 #endif
     lds->lds_syslog_ident = "ompi";
@@ -154,7 +154,7 @@ static void parse_verbose(char *e, opal_output_stream_t *lds)
     }
 
     if (0 == strcasecmp(ptr, "syslog")) {
-#ifndef WIN32 /* there is no syslog */
+#ifndef __WINDOWS__  /* there is no syslog */
 		lds->lds_want_syslog = true;
       have_output = true;
     }
diff --git a/opal/memoryhooks/memory.c b/opal/memoryhooks/memory.c
index 9b8b12ac07..84e9abc2eb 100644
--- a/opal/memoryhooks/memory.c
+++ b/opal/memoryhooks/memory.c
@@ -18,8 +18,12 @@
 
 #include "ompi_config.h"
 
+#ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
+#endif  /* HAVE_SYS_TYPES_H */
+#ifdef HAVE_SYS_MMAN_H
 #include <sys/mman.h>
+#endif  /* HAVE_SYS_MMAN_H */
 
 #include "opal/include/constants.h"
 #include "opal/util/output.h"
diff --git a/opal/runtime/opal_progress.c b/opal/runtime/opal_progress.c
index 627b187be7..c31fe90e76 100644
--- a/opal/runtime/opal_progress.c
+++ b/opal/runtime/opal_progress.c
@@ -295,7 +295,7 @@ opal_progress(void)
 #endif
     }
 
-#if !defined(WIN32) && defined(HAVE_SCHED_YIELD)
+#if !defined(__WINDOWS__) && defined(HAVE_SCHED_YIELD)
     if (call_yield && events <= 0) {
         /* If there is nothing to do - yield the processor - otherwise
          * we could consume the processor for the entire time slice. If
diff --git a/opal/threads/mutex.c b/opal/threads/mutex.c
index d6068149d9..d11e010470 100644
--- a/opal/threads/mutex.c
+++ b/opal/threads/mutex.c
@@ -26,7 +26,7 @@
 bool opal_uses_threads = (bool) OMPI_HAVE_THREAD_SUPPORT;
 
 
-#ifdef WIN32
+#ifdef __WINDOWS__
 
 #include <windows.h>
 
diff --git a/opal/threads/thread.c b/opal/threads/thread.c
index 85610da8ef..68c69915d0 100644
--- a/opal/threads/thread.c
+++ b/opal/threads/thread.c
@@ -45,7 +45,7 @@ static void opal_thread_construct(opal_thread_t *t)
 }
 
 
-#if defined(WIN32)
+#ifdef __WINDOWS__
 
 /************************************************************************
  * Windows threads
diff --git a/opal/threads/threads.h b/opal/threads/threads.h
index 2ea5ddb0d7..0d705b9e99 100644
--- a/opal/threads/threads.h
+++ b/opal/threads/threads.h
@@ -19,7 +19,7 @@
 #ifndef OPAL_THREAD_H
 #define OPAL_THREAD_H 1
 
-#ifdef WIN32
+#ifdef __WINDOWS__
 #include <windows.h>
 #elif OMPI_HAVE_POSIX_THREADS
 #include <pthread.h>
@@ -39,7 +39,7 @@ struct opal_thread_t {
     opal_object_t super;
     opal_thread_fn_t t_run;
     void* t_arg;
-#ifdef WIN32
+#ifdef __WINDOWS__
     HANDLE t_handle;
 #elif OMPI_HAVE_POSIX_THREADS
     pthread_t t_handle;
diff --git a/opal/util/argv.c b/opal/util/argv.c
index aab9d1d946..b8d4935a73 100644
--- a/opal/util/argv.c
+++ b/opal/util/argv.c
@@ -17,8 +17,12 @@
  */
 
 #include "ompi_config.h"
+#ifdef HAVE_STDLIB_H
 #include <stdlib.h>
+#endif  /* HAVE_STDLIB_H */
+#ifdef HAVE_STRING_H
 #include <string.h>
+#endif  /* HAVE_STRING_H */
 
 #include "opal/util/argv.h"
 #include "opal/util/strncpy.h"
diff --git a/opal/util/basename.c b/opal/util/basename.c
index d335d28c9f..52e55b6f0d 100644
--- a/opal/util/basename.c
+++ b/opal/util/basename.c
@@ -29,7 +29,7 @@ char *opal_basename(const char *filename)
 {
     size_t i;
     char *tmp, *ret = NULL;
-#ifdef WIN32
+#ifdef __WINDOWS__
     const char sep = '\\';
 #else
     const char sep = '/';
@@ -43,7 +43,7 @@ char *opal_basename(const char *filename)
 
     /* On Windows, automatically exclude a drive designator */
 
-#ifdef WIN32
+#ifdef __WINDOWS__
     if (strlen(filename) == 2 &&
         isalpha(filename[0]) && ':' == filename[1]) {
         return strdup(filename);
diff --git a/opal/util/crc.c b/opal/util/crc.c
index c6909caf2e..9d15ad84f5 100644
--- a/opal/util/crc.c
+++ b/opal/util/crc.c
@@ -19,10 +19,18 @@
 
 #include "ompi_config.h"
 #include <stdio.h>
+#ifdef HAVE_STDLIB_H
 #include <stdlib.h>
+#endif  /* HAVE_STDLIB_H */
+#ifdef HAVE_STRINGS_H
 #include <strings.h>
+#endif  /* HAVE_STRINGS_H */
+#ifdef HAVE_STRING_H
 #include <string.h>
+#endif  /* HAVE_STRING_H */
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
+#endif  /* HAVE_UNISTD_H */
 #include "opal/util/crc.h"
 
 
diff --git a/opal/util/daemon_init.c b/opal/util/daemon_init.c
index cee7e9e4d7..26be7a7ff9 100644
--- a/opal/util/daemon_init.c
+++ b/opal/util/daemon_init.c
@@ -35,7 +35,7 @@
 int opal_daemon_init(char *working_dir)
 {
 #if defined(HAVE_FORK)
-#ifndef WIN32
+#ifndef __WINDOWS__
     /* it seems that there is an entirely different way to write daemons in 
        WINDOWS land. Firstly, they are called services and the way to 
        go about it is to get a service handle annd then call CreateService()
diff --git a/opal/util/few.c b/opal/util/few.c
index 4ff3b57b09..45b7d3d7b5 100644
--- a/opal/util/few.c
+++ b/opal/util/few.c
@@ -34,7 +34,7 @@
 
 int opal_few(char *argv[], int *status)
 {
-#ifndef WIN32
+#ifndef __WINDOWS__
 #if defined(HAVE_FORK) && defined(HAVE_EXECVE) && defined(HAVE_WAITPID)
     pid_t pid, ret;
 
diff --git a/opal/util/if.c b/opal/util/if.c
index 2a05fe2941..3a585c6e8f 100644
--- a/opal/util/if.c
+++ b/opal/util/if.c
@@ -84,7 +84,7 @@ struct opal_if_t {
     opal_list_item_t     super;
     char                if_name[IF_NAMESIZE];
     int                 if_index;
-#ifndef WIN32
+#ifndef __WINDOWS__
     int                 if_flags;
 #else
     u_long              if_flags;
@@ -92,7 +92,7 @@ struct opal_if_t {
     int                 if_speed;
     struct sockaddr_in  if_addr;
     struct sockaddr_in  if_mask;
-#ifdef WIN32
+#ifdef __WINDOWS__
     struct sockaddr_in  if_bcast;
 #endif
     uint32_t            if_bandwidth;
@@ -111,7 +111,7 @@ static bool already_done = false;
 
 static int opal_ifinit(void) 
 {
-#ifndef WIN32
+#ifndef __WINDOWS__
     int sd;
     int lastlen, num, rem;
     char *ptr;
@@ -284,7 +284,7 @@ static int opal_ifinit(void)
     free(ifconf.ifc_req);
     close(sd);
     
-#else /* WIN32 implementation begins */
+#else /* __WINDOWS__ implementation begins */
 
     /* 
        1. check if the interface info list is already populated. If so, return
@@ -395,7 +395,7 @@ static int opal_ifinit(void)
 int opal_iffinalize(void) 
 {
     if (already_done) {
-#ifndef WIN32
+#ifndef __WINDOWS__
         opal_if_t *intf_ptr;
     
         while (NULL != 
@@ -465,7 +465,7 @@ int opal_ifnametoindex(const char* if_name)
 int opal_ifaddrtoname(const char* if_addr, char* if_name, int length)
 {
     opal_if_t* intf;
-#ifndef WIN32
+#ifndef __WINDOWS__
     in_addr_t inaddr;
 #else 
     unsigned long inaddr;
diff --git a/opal/util/os_create_dirpath.c b/opal/util/os_create_dirpath.c
index 60ea477aef..3a50540aed 100644
--- a/opal/util/os_create_dirpath.c
+++ b/opal/util/os_create_dirpath.c
@@ -32,7 +32,7 @@
 #include "opal/util/argv.h"
 #include "ompi/include/constants.h"
 
-#ifdef WIN32
+#ifdef __WINDOWS__
 #define PATH_SEP "\\"
 #else
 #define PATH_SEP "/"
@@ -100,7 +100,7 @@ int opal_os_create_dirpath(const char *path, const mode_t mode)
     for (i = 0; i < len; ++i) {
         if (i == 0) {
 
-#ifdef WIN32         
+#ifdef __WINDOWS__
             /* In the Windows case, check for "<drive>:" case (i.e.,
                an absolute pathname).  If this is the case, ensure
                that it ends in a path_sep. */
diff --git a/opal/util/os_path.c b/opal/util/os_path.c
index 4b22a77c4f..d23992e837 100644
--- a/opal/util/os_path.c
+++ b/opal/util/os_path.c
@@ -34,7 +34,7 @@
 #include "opal/util/os_path.h"
 #include "ompi/include/constants.h"
 
-#ifdef WIN32
+#ifdef __WINDOWS__
 #define PATH_SEP "\\"
 #else
 #define PATH_SEP "/"
@@ -70,7 +70,7 @@ char *opal_os_path(bool relative, ...)
             strcat(path, path_sep);
     	}
     	else {
-#ifndef WIN32
+#ifndef __WINDOWS__
     	    strcpy(path, path_sep);
 #endif
     	}
diff --git a/opal/util/path.c b/opal/util/path.c
index c09ee915fc..6c5b467ce0 100644
--- a/opal/util/path.c
+++ b/opal/util/path.c
@@ -29,7 +29,7 @@
 /*
  * PATH environment variable separator
  */
-#ifdef WIN32
+#ifdef __WINDOWS__
 #define PATHENVSEP  ';'
 #else
 #define PATHENVSEP  ':'
diff --git a/opal/util/stacktrace.c b/opal/util/stacktrace.c
index 88275266af..61cac8e0e2 100644
--- a/opal/util/stacktrace.c
+++ b/opal/util/stacktrace.c
@@ -59,7 +59,7 @@
  *
  * FIXME: Should distinguish for systems, which don't have siginfo...
  */
-#if OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(WIN32)
+#if OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(__WINDOWS__)
 static void opal_show_stackframe (int signo, siginfo_t * info, void * p)
 {   
 #ifdef HAVE_BACKTRACE
@@ -290,7 +290,7 @@ static void opal_show_stackframe (int signo, siginfo_t * info, void * p)
     fflush(stderr);
 }
 
-#endif /* OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(WIN32) */
+#endif /* OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(__WINDOWS__) */
 
 
 /**
@@ -305,7 +305,7 @@ static void opal_show_stackframe (int signo, siginfo_t * info, void * p)
  */
 int opal_util_register_stackhandlers (void)
 {
-#if OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(WIN32)
+#if OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(__WINDOWS__)
     struct sigaction act;
     char * string_value;
     char * tmp;
@@ -350,7 +350,7 @@ int opal_util_register_stackhandlers (void)
         return OMPI_ERR_IN_ERRNO;
       }
     }
-#endif /* OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(WIN32) */
+#endif /* OMPI_WANT_PRETTY_PRINT_STACKTRACE && ! defined(__WINDOWS__) */
 
     return OMPI_SUCCESS;
 }