diff --git a/Xos.h b/Xos.h
index b6b93a5..67bf679 100644
--- a/Xos.h
+++ b/Xos.h
@@ -149,7 +149,7 @@ extern int sys_nerr;
  */
 #if defined(X_NOT_POSIX)
 #include <fcntl.h>
-#if defined(USL) || defined(CRAY) || defined(MOTOROLA) || (defined(i386) && (defined(SYSV) || defined(SVR4))) || defined(__sxg__)
+#if defined(USL) || defined(CRAY) || defined(MOTOROLA) || (defined(__i386__) && (defined(SYSV) || defined(SVR4))) || defined(__sxg__)
 #include <unistd.h>
 #endif
 #ifdef WIN32
diff --git a/Xos_r.h b/Xos_r.h
index f52bde7..7ce72ac 100644
--- a/Xos_r.h
+++ b/Xos_r.h
@@ -237,7 +237,7 @@ extern void XtProcessUnlock(
 
 #elif !defined(XTHREADS) && !defined(X_FORCE_USE_MTSAFE_API)
 /* Use regular, unsafe API. */
-# if defined(X_NOT_POSIX) && !defined(i386) && !defined(SYSV)
+# if defined(X_NOT_POSIX) && !defined(__i386__) && !defined(SYSV)
 extern struct passwd *getpwuid(), *getpwnam();
 # endif
 typedef int _Xgetpwparams;	/* dummy */
diff --git a/Xosdefs.h b/Xosdefs.h
index be90d5e..14971c4 100644
--- a/Xosdefs.h
+++ b/Xosdefs.h
@@ -86,7 +86,7 @@ in this Software without prior written authorization from The Open Group.
 #endif
 #endif
 
-#ifdef i386
+#ifdef __i386__
 #ifdef SYSV
 #if !defined(ISC) && !defined(__SCO__) && !defined(_SEQUENT_) && \
 	!defined(__UNIXWARE__) && !defined(sun)