https://bird.network.cz/pipermail/bird-users/2020-February/014211.html

diff --git a/nest/route.h b/nest/route.h
index d2a07f09..b927db5f 100644
--- a/nest/route.h
+++ b/nest/route.h
@@ -458,7 +458,7 @@ typedef struct rta {
 					   protocol-specific metric is availabe */
 
 
-const char * rta_dest_names[RTD_MAX];
+extern const char * rta_dest_names[RTD_MAX];
 
 static inline const char *rta_dest_name(uint n)
 { return (n < RTD_MAX) ? rta_dest_names[n] : "???"; }