--- contrib/libs/libidn/lib/idna.h
+++ contrib/libs/libidn/lib/idna.h
@@ -99,6 +99,10 @@ extern "C"
 #  define IDNA_ACE_PREFIX "xn--"
 # endif
 
+# ifndef IDNA_LABEL_MAX_LENGTH
+#  define IDNA_LABEL_MAX_LENGTH 255
+# endif
+
   extern IDNAPI const char *idna_strerror (Idna_rc rc);
 
   /* Core functions */