# ifndef ossl_ssize_t
# define ossl_ssize_t ssize_t
-# define OSSL_SSIZE_MAX SSIZE_MAX
+# if defined(SSIZE_MAX)
+# define OSSL_SSIZE_MAX SSIZE_MAX
+# elif defined(_POSIX_SSIZE_MAX)
+# define OSSL_SSIZE_MAX _POSIX_SSIZE_MAX
+# endif
# endif
# ifdef DEBUG_UNUSED