diff --git a/e_os.h b/e_os.h
index 700d7d05ce..4951335635 100644
--- a/e_os.h
+++ b/e_os.h
@@ -473,7 +473,9 @@ struct servent *PASCAL getservbyname(const char *, const char *);
 #   define open _open
 #   define fdopen _fdopen
 #   define close _close
-#   define strdup _strdup
+#   ifndef strdup
+#    define strdup _strdup
+#   endif
 #   define unlink _unlink
 #  endif
 # else