diff --git a/nest/route.h b/nest/route.h
index c23dcc10..377874f0 100644
--- a/nest/route.h
+++ b/nest/route.h
@@ -81,7 +81,7 @@ void fib_delete(struct fib *, void *);	/* Remove fib entry */
 void fib_free(struct fib *);		/* Destroy the fib */
 void fib_check(struct fib *);		/* Consistency check for debugging */
 
-void fit_init(struct fib_iterator *, struct fib *); /* Internal functions, don't call */
+void fit_init(struct fib_iterator *, const struct fib *); /* Internal functions, don't call */
 struct fib_node *fit_get(struct fib *, struct fib_iterator *);
 void fit_put(struct fib_iterator *, struct fib_node *);
 void fit_put_next(struct fib *f, struct fib_iterator *i, struct fib_node *n, uint hpos);
diff --git a/nest/rt-fib.c b/nest/rt-fib.c
index 8021ea24..6ee7b2a5 100644
--- a/nest/rt-fib.c
+++ b/nest/rt-fib.c
@@ -446,7 +446,7 @@ fib_free(struct fib *f)
 }
 
 void
-fit_init(struct fib_iterator *i, struct fib *f)
+fit_init(struct fib_iterator *i, const struct fib *f)
 {
   unsigned h;
   struct fib_node *n;