diff --git a/defines.h b/defines.h
index 3ac8be987..f489196ed 100644
--- a/defines.h
+++ b/defines.h
@@ -105,6 +105,14 @@ enum
 # endif /* PATH_MAX */
 #endif /* MAXPATHLEN */
 
+#ifndef HOST_NAME_MAX
+# if defined(_POSIX_HOST_NAME_MAX)
+#  define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
+# elif defined(MAXHOSTNAMELEN)
+#  define HOST_NAME_MAX MAXHOSTNAMELEN
+# endif
+#endif /* HOST_NAME_MAX */
+
 #if defined(HAVE_DECL_MAXSYMLINKS) && HAVE_DECL_MAXSYMLINKS == 0
 # define MAXSYMLINKS 5
 #endif