diff --git a/mlibc/include/ctype.h b/mlibc/include/ctype.h
index d6e961c2..69d1210c 100644
--- a/mlibc/include/ctype.h
+++ b/mlibc/include/ctype.h
@@ -28,6 +28,7 @@
 #include_next <ctype.h>
 
 #else // ! (__GNUC__ && POSIX)
+#include <endian.h>
 int isdigit (int);
 int isxdigit (int);
 #endif // ! (__GNUC__ && POSIX)
diff --git a/mlibc/include/endian.h b/mlibc/include/endian.h
new file mode 100644
index 00000000..87d10117
--- /dev/null
+++ b/mlibc/include/endian.h
@@ -0,0 +1,36 @@
+/* -*-comment-start: "//";comment-end:""-*-
+ * Mes --- Maxwell Equations of Software
+ * Copyright © 2017 Jan Nieuwenhuizen <janneke@gnu.org>
+ *
+ * This file is part of Mes.
+ *
+ * Mes is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Mes is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Mes.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef __MES_ENDIAN_H
+#define __MES_ENDIAN_H 1
+
+#if __GNUC__ && POSIX
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#undef __MES_ENDIAN_H
+#include_next <endian.h>
+
+#else // ! (__GNUC__ && POSIX)
+#define	__LITTLE_ENDIAN 1234
+#define	__BIG_ENDIAN 4321
+#define __BYTE_ORDER __LITTLE_ENDIAN
+#endif // ! (__GNUC__ && POSIX)
+
+#endif // __MES_ENDIAN_H
diff --git a/mlibc/include/stdlib.h b/mlibc/include/stdlib.h
index a6719adc..cb9f0a8c 100644
--- a/mlibc/include/stdlib.h
+++ b/mlibc/include/stdlib.h
@@ -49,6 +49,8 @@ unsigned long long strtoull (char const *nptr, char **endptr, int base);
 #define EXIT_FAILURE 1
 #define EXIT_SUCCESS 0
 
+#include <endian.h>
+
 #endif // !(__GNUC__ && POSIX)
 
 #endif // __MES_STDLIB_H
diff --git a/mlibc/include/sys/types.h b/mlibc/include/sys/types.h
index d2f1620c..4e00b73e 100644
--- a/mlibc/include/sys/types.h
+++ b/mlibc/include/sys/types.h
@@ -23,7 +23,9 @@
 #if __GNUC__ && POSIX
 #undef __MES_SYS_TYPES_H
 #include_next <sys/types.h>
-#endif // (__GNUC__ && POSIX)
+#else // ! (__GNUC__ && POSIX)
+#include <endian.h>
+#endif // ! (__GNUC__ && POSIX)
 
 #endif // __MES_SYS_TYPES_H